They had assumed chemical signals from tears would trigger sadness or empathy in others. But initial experiments found that sniffing women’s tears did not affect men’s mood or empathy, but “had a pronounced influence on sexual arousal, a surprise,” Dr. Sobel said.

Deciding to investigate more rigorously, the researchers posted fliers on several Israeli college campuses seeking easy criers. Seventy women volunteered, along with one man. But of the 70 women, there were only six “who were really good” at bawling their eyes out, Dr. Sobel said. They became the researchers’ “bank of criers”; a stable of “backup criers” was kept in reserve.

Image Tears of “really good” criers were collected and dribbled on pads that were placed under men’s noses to approximate a hug. Credit... Science/AAAS

“We had to use fresh tears,” no more than two hours old, Dr. Sobel said, and frozen would not do. So the criers were called on frequently to sob a renewed supply, a milliliter each time. The women, who were in their late 20s and early 30s, watched scenes from Hollywood tear-jerkers like “My Sister’s Keeper” and “When a Man Loves a Woman” and one from Israel, “Broken Wings,” said Yaara Yeshurun, a doctoral student on the team. Ms. Yeshurun was also one of the criers, losing it over “Terms of Endearment.”

As a control, researchers trickled saline down the women’s faces, also collecting that in vials. Tears and saline were dribbled onto pads that were then affixed below men’s nostrils to approximate a hug with a teary woman. The men, in their late 20s, each sniffed tears one day and saline another day, without knowing which was which.

In one experiment, tear-sniffing made the men more likely to rate women in photographs as less sexually attractive. In another, to establish a context of sadness, men watched a scene from the movie “The Champ” after sniffing tears or saline. Sniffers became equally sad with both tears and saline, but tear-sniffers showed reduced sexual arousal and lower levels of testosterone.

Finally, the researchers turned to brain imaging. They showed men scenes from “9 ½ Weeks”  specifically the more explicit version that was shown in Europe, which, Dr. Sobel said, “has been validated as being particularly arousing.” Functional M.R.I. scans identified the men’s arousal in specific brain areas. Then they sniffed tears or saline and watched sad movies. The tear-sniffers showed less activity in the brain regions that reflected arousal.