Through this experiment, and several others, the team has shown that sex is a pleasurable experience for flies—or specifically, that ejaculation is for the males. It releases the same chemicals that are linked to rewarding experiences in mammals. It creates associations that make other stimuli occurring at the same time—like a smell—desirable in their own right. It even substitutes for other rewards: Male flies that have recently ejaculated are less enticed by alcohol.

This might seem obvious, but the study of animal sex tends to be curiously sanitized and anhedonic. The focus falls on the mechanics of the act and its evolutionary benefits, while subjective experiences are ignored for fear of anthropomorphism. It is often said that humans are among the only animals that have sex “for pleasure”—an elite club that might grudgingly include bonobos and dolphins, but little else. And even if the idea that animals are enjoying themselves is not explicitly denied, it’s often just plain ignored. Animal sex becomes all business, and no ... well, you know.

That seems unlikely. Many animals have sex at times when they’re infertile or in ways that can’t possibly lead to reproduction. Several species practice oral sex, including bonobos (of course), brown bears (in captivity), and several kinds of bat (the music choice in this video is something). A lot of them masturbate. “I definitely think animals have pleasure,” says Shohat-Ophir. “It’s hard if you define pleasure from a human point of view, but it [comes down to] very basic machinery that even simpler animals have.”

For example, when flies mate, their brains accumulate a substance called neuropeptide F, which acts as a “molecular signature of rewarding experiences,” Shohat-Ophir says. Even without mating, a burst of corazonin, stimulated by red light, can produce the same burst of NPF.

“Think of the reward system as a reservoir and NPF as a float that measures the amount within it,” says Shohat-Ophir. When levels are low, the insects are more motivated to top up their reservoirs by seeking out rewarding experiences. For instance, in an earlier study, her team found that sex-deprived flies will more readily turn to alcohol. (No barfly jokes, please; since these flies eat fermented fruit, alcohol is a natural part of their diet.) And in the team’s latest experiments, they found that a burst of corazonin can quell that desire. After ejaculating, males will choose a sober meal over a boozy one.

“For the first time, we see that neurons outside the brain can induce feelings of reward, which change the internal state of the animal, and changes their perception of a drug,” says Shohat-Ophir.

This isn’t just about flies. Mammals have a closely related chemical called neuropeptide Y that could similarly act as a mental currency of reward. In rodents, NPY is depleted by stressful events and leads to cravings for alcohol. Other scientists are already looking to see if NPY levels are linked to alcoholism or drug addiction.