Cutaneous Stimuli Wild rats display with some regularity four types of behavior, besides huddling, which involve mutual cutaneous stimulation. The most distinctive is "crawling under". This act is accurately described by it's name. It is performed by both norvegicus and rattus, and has been observed especially among males in situations which might lead to conflict. For instance, if a strange male approaches a non-aggressive male in the latter's territory, the resident may crawl under the stranger. A stranger may also crawl under a resident. Crawling under is often seen among young rats, during play. A second, and allied type of act may be called "walking over". This expression, again accurately descriptive, refers to an act which no doubt often takes place incidentally, but which certainly is also carried out as a specific response to the presence of another rat. Observations shows that rats often literally go out of their way to crawl under or walk over other members of their colony. A third type of contact behavior is "mutual grooming". This consists of gentle nibbling of the fur on any accessible area of skin. Like crawling under, it is seen mainly in conflict situations, but it is not confined to them. Fourth, and last of the distinctive acts under this heading, is "nosing", in which one rat gently pushes with it's nose at the flank, usually near the neck, of another rat. THis is seen in a variety of situations, including that in which a female in estrus approaches a male. Source: the book "The Rat: A Study in Behaviour" by S.A. Barnett