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Rodents typically show conditioned aversions to substances previously associated with illness. Aversions can be observed when the tastant is presented in food, water and, for rats, when the tastant is smeared unilaterally on the animal's flank and ingested during auto-grooming. Such results have important implications for rodent control. For that reason, others have investigated whether voles and mice continue to groom when tastants associated with sickness are smeared on their fur. Investigations have shown that grooming persists in the presence of the conditioned stimuli even though strong aversions are shown toward the same tastants in a drinking context. The question remains, however, whether conditioned aversions would be expressed in special situations. The present experiments clearly demonstrate that taste aversions can be observed during heterogrooming of a cagemate, but not during autogrooming of self. Such results suggest that social variables may modulate expression of conditioned taste aversions for some gregarious and/or communal species. Also, they are consistent with the notion that various species show specialized adaptive systems which may not obey conventional laws of learning.