Appellant Porter appeals from her conviction and life sentence for murder. The victim, stabbed some 65 times, was discovered in a motel room with her three-year-old daughter. On this appeal, we consider the exclusion of prospective jurors with scruples against the death penalty; the refusal of the trial court to permit the child to testify; and an improper reference by one witness to a polygraph test. We find no error and affirm the conviction.
1. Appellant argues that exclusion of death-scrupled jurors from the guilt phase of her trial, under the authority of Witherspoon v. Illinois, 391 U. S. 510 (1968), was unnecessary and deprived her of a valid cross section of the community on the issue of guilt. Appellant offered to accept a verdict on punishment by fewer than twelve, as a means of accommodating her request that jurors with scruples against the death penalty be permitted to serve during the guilt determination phase though the state would be entitled to disallow their participation in deciding punishment. The trial court refused this request.
Traditionally, this court has simply ruled that an appellant not sentenced to death is without standing to raise this issue. E. g., Lindsey v. State, 234 Ga. 874, 875 (218 SE2d 585)(1975); Davis v. State, 234 Ga. 730, 731 (218 SE2d 20) (1975). But we read the present argument to claim an unconstitutional jury on the guilt issue, which plainly appellant has standing to raise. Considered on the merits, however, the claim is unpersuasive because it argues that death-scrupled jurors constitute a *581recognizable class, representation of which is necessary on the guilt phase to grant a valid cross section of the community. This argument was specifically rejected by the Supreme Court in Witherspoon, supra, 391 U. S. at 518. Appellant cites Labat v. Bennett, 365 F2d 698 (5th Cir. 1966) which did indeed have broad "cross section” import at the time of its decision. See Note, 1967 Duke L. J. 346 (1967). But Witherspoon rejected such a reading with respect to death-scrupled jurymen as a class, where the guilt determination phase was involved. See Comment, Jury Challenges, Capital Punishment and Labat v. Bennett: A Reconciliation, 1968 Duke L. J. 283 (1968) cited in Witherspoon, supra, 391 U. S. at 515-516, n. 9.
Appellant’s jury was not unconstitutionally composed.
2. It appeared almost certain from the evidence that the victim’s three-year-old daughter Paula had been in the room with her mother during the murder. The trial court refused even to examine the child as a potential witness and ruled that she was incompetent because of infancy. Enumerations of error two and three argue that the requirements of due process and of Code Ann. § 38-1610 (requiring the court to examine witnesses to decide incompetency) mandate an examination and the court erred in presuming the child incompetent.
The competency of a witness is for the court to decide in its discretion (Code Ann. § 38-1601), and this decision will not be overturned in absence of abuse of discretion (Geter v. State, 231 Ga. 615, 617 (203 SE2d 195) (1974)). Children who do not understand the nature of an oath are incompetent. Code Ann. § 38-1607; Young v. State, 122 Ga. 725 (50 SE 996)(1905).
Based upon her father’s testimony of the child’s birth date, she was two years and eleven months old at the time of the killing, and three years and two months old at the time of the trial. There was testimony which tended to show her somewhat inappropriate responses and non-responses when others had addressed her after the discovery of the body.
On the record before us, we cannot conclude under Code Ann. § 38-1610, nor due process, nor Schamroth v. *582State, 84 Ga. App. 580 (66 SE2d 413) (1951), that the court erred in conclusively presuming this child incompetent. Appellant is correct in pointing to Fields v. State, 500 SW2d 500 (Tex. Crim. App. 1973), in which a four-year-old witness to murder was permitted to testify; and Wheeler v. United States, 159 U. S. 523 (1895) allowing a five-and-one-half-year-old witness. However, the United States Supreme Court in Wheeler wrote that ". . . no one would think of calling as a witness an infant only two or three years old. . .” 159 U. S. at 524.
These enumerations are without merit.
3. Deputy Cantrell’s mention of the word "polygraph” presents no issue of substance. The record shows that the most damaging evidence against appellant was given by one Lawless, who was originally charged with appellant for the crime but who testified for the state under a grant of immunity. Defense counsel was pressing Cantrell on the general subject of the time at which Lawless had begun to tell the story he told at trial, and, after 18 transcript pages of'cross examination, Cantrell testified "The first time Lawless ever gave any indication of knowing what has happened was immediately after we took a polygraph test and . . .” The testimony was interrupted; the jury was removed; the court refused to grant a mistrial or to allow any further mention of a polygraph test and refused defense requests to pursue the question whether Cantrell’s mention of the polygraph test was somehow a deliberate violation of the warnings to all witnesses. The jury upon their return was told to disregard the answer.
The refusal of the mistrial motion and of requested cross examination were not error. Cantrell’s statement did not say to whom the polygraph test was given, what was learned, whether the subject "passed” it or "failed” it, or anything of substance. The most the jury could have learned was that someone was given a polygraph test and thereafter Lawless admitted knowing something of what happened.
In Stack v. State, 234 Ga. 19 (214 SE2d 514) (1975) we reversed when a polygraph operator was permitted to testify to a conversation with defendant during the period when the test was being administered. But the Stack *583issues are not present here. As we wrote in Herlong v. State, 236 Ga. 326, 328 (223 SE2d 672) (1976), "The decision in Stack did not require, as a matter of law, that a new trial be granted on every occasion where a jury is apprised that a lie detector test has been given.” These enumerations are without merit. Accord, People v. Baker, 7 Mich. App. 471 (152 NW2d 43)(1967).
Argued April 13, 1976
Decided September 9, 1976
Rehearing denied September 28, 1976.
Murder. Whitfield Superior Court. Before Judge Vining.
Millard C. Farmer, Jr., for appellant.
Judgment affirmed.
All the Justices concur, except Jordan, J., who concurs in Divisions 1 and 3 and the judgment, Ingram, J., who dissents as to Division 2 and Gunter and Hill, JJ., who dissent as to Divisions 2 and 3.