Defendant first contends that the court erred in permitting the witness White to testify as to the authorship of a letter allegedly written by defendant’s witness James McDougal. McDougal testified that he saw the defendant on the morning of the robbery, that the defendant was not himself, and that he appeared to be sick and in pain. On cross-examination McDougal testified that he wanted to help defendant but that he would not do anything dishonest to do so. He denied writing a letter purporting to be from him to the prosecutrix, Loretta Williams, offering her $200 not to identify defendant as the robber. Following this denial, the State, for the purpose of impeachment, called Philip White, a documents examiner for the North Carolina Bureau of Investigation, as a witness. Mr. White testified, over objection, that in his opinion the letter received by Loretta offering her $200 not to identify the defendant as the robber was written by McDougal. The defendant contends that the questions concerning the letter were on a collateral matter and that the State was bound by McDougal’s answers.
 Ordinarily, a party is bound by the answer of the witness to a question asked on cross-examination as to a collateral matter. In re Gamble, 244 N.C. 149, 93 S.E. 2d 66; State v. King, 224 N.C. 329, 30 S.E. 2d 230; Stansbury, N. C. Evidence § 48 (2d ed., 1963); 7 Strong’s N. C. Index 2d, Witnesses § 8, p. 704. However, to this general rule there are exceptions. The rule *83does not apply when the questions tend to show bias, interest, or prejudice of the witness. In re Gamble, supra; State v. Hart, 239 N.C. 709, 80 S.E. 2d 901; State v. English, 201 N.C. 295, 159 S.E. 318; Stansbury, N. C. Evidence § 48 (2d ed., 1963); 7 Strong’s N. C. Index 2d, Witnesses § 8, p. 705.
In State v. English, supra, defendant was charged with the murder of his wife. The wife’s father testified for the defendant. The court held that evidence of the wife’s father’s attempt to bribe another witness was admissible to show the bias of the bribing witness for the defendant. The Court stated: “Exceptions were also taken to evidence tending to show that the father of the deceased woman, who was a witness for defendant, had attempted to bribe a colored man to implicate two other parties. These exceptions are not sustained. S. v. Patterson, 24 N.C. 346; S. v. Beal, 199 N.C. 278 [154 S.E. 604]."
Justice Ervin, in State v. Hart, supra, states the reason for the exception to the collateral matter rule as follows:
“Truth does not come to all witnesses in naked simplicity. It is likely to come to the biased or interested witness as the image of a rod comes to the beholder through the water, bent and distorted by his bias or interest. The law is mindful of this plain psychological principle when its fashions rules of evidence to aid jurors in their search after truth. As a consequence, the law decrees that ‘any evidence is competent which tends to show the feeling or bias of a witness in respect to the party or the cause,’ and that jurors are to consider and weigh evidence of this character in determining the credibility of the witness to whom it relates.
“Where a party cross-examines an adverse witness as to matters which tend to show the partiality of the witness for his adversary or the hostility of the witness toward him, the party is not bound by the answers of the witness denying partiality or hostility, but is at liberty to contradict the witness by the testimony of other persons disclosing such partiality or such hostility. (Citing cases.)”
 We hold that the testimony of the witness White was competent to show the bias or interest of defendant’s witness McDougal.
*84Defendant assigns as error various portions of the trial judge’s charge to the jury. The trial judge initially charged the jury on armed robbery as follows:
“Now ladies and gentlemen of the jury, the defendant in this case is charged with the crime of armed robbery. Armed robbery is the taking of personal property from another by the use of force or intimidation, and by means of a threat to the life of another, accompanied by the use of some weapon. This weapon must be in the possession of the accused at the time of the alleged offense. The State has the burden of convincing the jury beyond a reasonable doubt, one, that the accused took personal property from another or from the presence of another, in this case from the presence of another, in this case from the presence of Loretta Williams; two, that the accused used force or intimidation sufficient to create ah apprehensive (sic) of danger; three, that the accused was in possession of and used or threatened to use some weapon and in fact threatened the life of the person from whom the property was taken, or from whose presence it was taken; and, finally, that the accused at the time of the taking, must have had the felonious intent to permanently deprive the owner of that property, and to convert it to his own use, or at least to some use besides that of the owner.”
Later in the charge the trial judge further instructed the jury as follows:
“Ladies and gentlemen of the jury I charge you that if you find from the evidence and beyond a reasonable doubt, the burden being upon the State of North Carolina to so satisfy you, that on the 23rd day of March 1970, the accused, William Bailey, Jr., took personal property, in this case United States money, from Loretta Williams or from her presence, and if you further find that the accused William Bailey, Jr., at that time, used force or intimidation sufficient to create an apprehension of danger; and if you further find that at that time the accused was in possession of, and used or threatened to use some weapon, and in fact threatened the life of the victim; and you further find from the evidence and beyond a reasonable doubt that the accused at the time of the taking of the property, had in his mind the felonious intent permanently to deprive the *85owner of that property and to convert it to his own use, or at least to the use of another;_”
 Defendant contends that the court erred in its charge by stating that one of the elements of armed robbery was that “the accused used force or intimidation sufficient to create an apprehension of danger,” without charging that the force or intimidation must be caused by the use or threatened use of a dangerous weapon or firearm, implemént or means.
Eobbery is the taking, with intent to steal, of personal property of another, from his person or in his presence, without his consent or against his will, by violence or intimidation. State v. Smith, 268 N.C. 167, 150 S.E. 2d 194. G.S. 14-87 does not add to or substract from the common law offense of robbery except to provide that when firearms or other dangerous weapons are used more severe punishment may be imposed. State v. Smith, supra; State v. Stewart, 255 N.C. 571, 122 S.E. 2d 355.
Defendant cites as authority State v. Covington, 273 N.C. 690, 161 S.E. 2d 140, and State v. Rogers, 246 N.C. 611, 99 S.E. 2d 803. In Covington the trial court charged defendants could be convicted if they “ . . . used force or intimidation sufficient to create an apprehension of danger in the person from whom the property was taken . . . ” , but failed to add the additional element required by the statute, “by the use or threatened use of firearms or other dangerous weapon, implement or means.”
In Rogers the Court charged as to common law robbery and completely omitted any reference to the use of a weapon. Thus instant case is distinguishable from Covington and Rogers because here the trial judge in his final instruction on armed robbery added to the definition of common law robbery the following: “ . . . and if you further find that at the time the accused was in possession of and used or threatened to use some weapon, and in fact threatened the life of the victim . . .. ”
 Defendant further contends that the trial court’s use of the words “some weapon” rather than “firearms or other dangerous weapon” constituted prejudicial error. The court, at the beginning of the charge, read the bill of indictment, which charged that William Bailey, Jr., “ . . . having in his possession, and with the use and threatened use of firearms and other dan*86gerous weapon, implement and means, to wit, a pistol ...” did feloniously steal, take and carry away United States money of the value of $85. Later, the trial judge stated that the prosecuting witness testified that defendant used a pistol in the robbery and that defendant in his statement to the officers admitted that at the time of the robbery he used a blue steel, white handle .22 caliber revolver or pistol. We do not approve the substitution of the words “some weapon” for the words of the statute, but under the facts of this case we do not think that, standing alone, the use of these words would be such as to misinform or mislead the jury.
 However, defendant’s assignment of error to the failure of the trial court to instruct on and submit to the jury the lesser offense of common law robbery presents a more serious question.
The trial judge charged the jury that they could return a verdict of guilty as charged in the bill of indictment or a verdict of not guilty.
Common law robbery is a lesser included offense of armed robbery, and an indictment for armed robbery will support a conviction for common law robbery. When there is evidence of defendant’s guilt of common law robbery, it is error for the court to fail to submit the lesser offense to the jury. State v. Wenrich, 251 N.C. 460, 111 S.E. 2d 582; State v. Davis, 242 N.C. 476, 87 S.E. 2d 906; State v. Hicks, 241 N.C. 156, 84 S.E. 2d 545; State v. Keller, 214 N.C. 447, 199 S.E. 620.
In State v. Hicks, supra, it is stated:
“ . . . The necessity for instructing the jury as to an included crime of lesser degree than that charged arises when and only when there is evidence from which the jury could find that such included crime of lesser degree was committed. The presence of such evidence is the determinative factor. Hence, there is no such necessity if the State’s evidence tends to show a completed robbery and there is no conflicting evidence relating to elements of the crime charged. Mere contention that the jury might accept the State’s evidence in part and might reject it in part will not suffice.”
*87Here, the State’s witness Loretta Williams testified that defendant robbed her by use of a pistol. On cross-examination she said that she did not know whether it was a “real or toy pistol.” The State offered defendant’s confession, which contained a statement by defendant that he used a .22 caliber pistol to rob Loretta Williams. However, defendant testified before the jury that because of the effect of wine and heroin in his system he passed out about noon on the day the crime was committed and remembered nothing until he was awakened that night by friends. He specifically denied any recollection of the alleged robbery or the possession by him of a pistol.
This conflicting testimony raised an issue for the jury as to whether defendant had in his possession and used or threatened to use a firearm or other dangerous weapon to perpetrate the robbery.
 The critical and essential difference between armed robbery and common law robbery is that in order for the jury to convict for armed robbery the victim must be endangered or threatened by the use or threatened use of a “firearm or other dangerous weapon, implement or means.” State v. Covington, supra.
Thus, the trial judge, even without request for special instructions, should have submitted the lesser offense of common law robbery to the jury under proper instructions. State v. Covington, supra; State v. Keller, supra; State v. Rogers, supra,; 61 A.L.R. 2d 996.
We do not deem it necessary to discuss the other assignments of error since there must be a new trial for error in the charge.