the 22-khz vocalizations of adults and the 40-khz vocalizations of pups are emitted in response to aversive situations or noxious stimuli. for example, isolation, aggression between males, appearance of predators, surprising noises and inescapable foot shocks would elicit these vocalizations. conversely, the 50-khz vocalizations emitted by adults are produced during appetitive situations such as social play between juveniles, whilst engaging in mating behaviour, or when the animal is touched gently. individual differences, as well as social factors such as housing arrangements, can affect the number of elicited vocalizations and the probability of their occurrence. however, variability is wider in 22- and 50-khz calls, and lower in 40-khz calls. whereas 40-khz calls have a high survival value for pups, 22- and 50-khz calls are emitted in situations that can differ greatly between individuals.