SANTA MONICA, Calif. (AP) _ A judge suddenly stopped an expert's explanation of DNA tests in the O.J. Simpson wrongful death trial Thursday, saying the defense cross-examination was putting one or more jurors to sleep.

The judge interrupted Robin Cotton's testimony as she was being asked by lawyer Robert Blasier about whose initials were on various containers of evidence _ an issue in the defense frame-up theory.

``Ladies and gentlemen,'' Superior Court Judge Hiroshi Fujisaki said. ``This scintillating examination is having an effect on our jurors _ at least one of them _ so we'd better take a recess.''

Defense lawyers were clearly upset by the judge's remark and rushed to his bench for a conference. After the break, Fujisaki summoned jurors and apologized for his sarcasm.

``I want to apologize to Mr. Blasier for calling the examination `scintillating,''' the judge said.

He told jurors that DNA testimony involves numbers and ``numbers are dry.''

He urged them to let him know if they became drowsy again because Blasier ``doesn't want to have his effort wasted if you are not listening.''

``If you feel yourself drifting off, raise your hand or something,'' Fujisaki said.

He also warned the jurors that people are watching them. ``If you feel you concentrate better by closing your eyes, have some second thoughts,'' the judge said, drawing chuckles in the courtroom.

It was the second time this week Fujisaki has had to warn jurors to pay attention. Earlier, he caught them averting their eyes from grisly autopsy photos.

Nodding jurors would be a worry to both sides since the plaintiffs are laying out evidence in precise detail and the defense is setting the stage for its claims of contamination and conspiracy.

Simpson, acquitted of murder last year but sued by the families of Nicole Brown Simpson and Ronald Goldman for wrongful death, was not in court Thursday. He was with his mother, Eunice, who was undergoing knee replacement surgery.

Cotton, who testified at Simpson's criminal trial, came up with a new interpretation of results that could deflate the defense theory that blood drops were planted on a pair of socks found in Simpson's bedroom.

Cotton, director of Cellmark Diagnostics in Maryland, repeated her criminal trial testimony that Ms. Simpson's blood had the same genetic markers as blood found on the sock.

But then she added that blood on the socks was a different quality _ not as degraded _ as a sample of Ms. Simpson's blood provided for comparison.

Blasier sought to cast doubt on the DNA evidence, noting that one test by Cotton's lab magnifies not only DNA but also any contaminants in the blood sample. Cotton conceded that was possible.

Cotton also conceded that her conclusion that Simpson's DNA markers occur in only 1-in-170-million people were based on tests of only 200 individuals, and that there were only two blacks in her sample.

``And that's the data from which you get one-in-170-million?'' Blasier asked.

``Yes,'' Cotton said.

``No further questions,'' Blasier said.

Later, two California Department of Justice scientists, Gary Sims and Renee Montgomery, gave even more astronomical figures pointing to Simpson's blood on the back gate of Ms. Simpson's condominium and on a sock found in his bedroom.