Rats Make a Special Sound When They Eat Chocolate
Friday, October 16, 2026204 words3 minutes172 reads
Scientists want ways to study positive emotional states in animals that cannot describe their feelings. Researchers from the University of Fukui and other Japanese institutions studied ultrasonic vocalizations in male rats eating chocolate. A machine-learning method distinguished a 40-kilohertz, inverted-U-shaped call from other calls.
The new call was tightly linked in time to chocolate feeding: 97.2% occurred within one second of biting or chewing. It was also significantly more frequent during chocolate consumption than during regular chow eating, even though the rats ate similar amounts of the two foods. This makes a simple explanation less likely: that the sound is caused only by chewing.
The team gave the rats naloxone, which blocks opioid receptors. It reduced the calls during chocolate eating, and it also reduced chocolate consumption. This finding suggests that the body's opioid system helps regulate the calls, but it does not prove that each call measures pleasure alone.
An important limitation remains. Rats were housed and recorded in pairs, and the researchers could not identify the individual animal making each sound. Calls could relate to feeding, taste, social conditions, or other internal states. The study offers a possible non-invasive behavioral signal for future research, not a way to read a rat's mind.
