A few years ago, Jaak Panksepp was able to show that rats, when tickled, were laughing in the ultrasonic 50-kHz high-frequency. In the present article, Rygula and his colleagues used this behavioural trait to analyse an “optimistic” behaviour in rats. They trained rats in operant Skinner boxes to press one lever in response to one tone to receive a food reward and to press another lever in response to a different tone to avoid punishment by electric foot shock. Once the rats mastered this task, the submitted them to tickling sessions allowing to distinguish rats which, when tickled, laughed a lot and less responsive rats (“non-laughing when tickled” group). When submitted to an ambiguous tone (intermediate between the two training tones) laughing rats pressed the (positive) food rewarded lever more likely than less responsive rats, a measure of the “optimistic” behaviour of laughing rats, an optimistic behavioural bias to the ambiguous cue. This method of deciphering emotional-cognitive changes in animals by submitting them to an ambiguous situation is extremely elegant and shows how refined can be modern behavioural studies.