Male intruder rats were placed individually into the cage of an established resident on 2 occasions separated by a 7–8 day interval. Residents readily attacked intruders and both animals lost weight during the first encounter. In contrast, no serious fighting occurred on the second encounter, and both intruders and residents maintained their body weight during the 24‐hr test. Observation of the intruder's behavior during the first 30 min of each encounter indicated that defensive‐submissive postures represent a response to an attack that only temporarily inhibits aggression whereas the emission of 22 kHz calls by the intruder is associated with a relatively permanent decrease in the resident animal's aggressive response.

The critical determinants of extended diurnal death feigning were assessed in a refinement experiment in which visual and tactile cues during rearing and/or testing were systematically eliminated. Ninety-five domestic chicks were reared in either a social environment or physical (tactile) isolation, and half in each rearing condition were reared and/or tested under conditions of visual restriction. As expected, social rearing was prerequisite to the manifestation of extended death feigning; however, the incidence and duration of death-feigning was attenuated by functional visual isolation of socially reared chicks during either rearing or testing. It was concluded that visual novelty of the environment is the minimal condition for sustained death feigning by young chicks in the daylight hours.