Grooming:

"In short, self-grooming probably is about hygiene and only hygiene, whereas social grooming seems to have more to do with relationships. The principal evidence to support that claim comes from two facts. One is that social grooming time correlates strongly with social group size (Fig. 4), a finding that has also been replicated for allopreening in birds (Radford and Du Plessis, 2008). Second, grooming is far from random within social groups: grooming partnerships tend to be consistent as well as persistent through time."

RIM Dunbar, The social role of touch in humans and primates: Behavioural function and neurobiological mechanisms

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"In fact, it seems that physical touch has emotional and social connotations that often far outweigh anything that can be expressed in language (Burgoon, 1991; Burgoon et al., 1992; Bottoroff, 1993; Dunbar, 2004). Touch can often convey the real meaning or intention of an interaction in a way that the accompanying speech simply cannot do. To coin a phrase, a touch is worth a thousand words."

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"Although the kinds of relationships found in primates clearly impose a significant cognitive demand, it is nonetheless equally clear that the cognitive dimension does not provide a complete explanation of what is involved in such relationships (Dunbar, in press). Indeed, our own experience of human relationships is that more is involved than just strategic thinking. Work on the social psychology of human friendships over the past decade or so suggests that relationships involve two independent dimensions that are usually described as ‘‘behaving close’’ and ‘‘feeling close’’ (Aron et al., 1992; Depue and Morrone-Strupinsky, 2005). Behaving close clearly accords with the suggestion that pairbonds rely on close behavioural coordination. In contrast, feeling close seems to point to something at the emotional level that is less easy to define because we ourselves often have difficulty verbalizing about it: it is something that quite literally we feel rather than cognize about (Dunbar, in press). It is in respect of this second component that grooming seems to play such a crucial role in primates."

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"a factor analysis of six different measures of closeness, including the RCI, identified a two-factor model whose elements were labelled ‘feeling close’ and ‘behaving close’(Aron et al. 1992). Aron et al. argued that there are two underlying types of closeness: subjective closeness (‘feeling close’) and an objective closeness (‘behaving close’). These do not necessarily bear a close relation to each other: you may have frequent interactions with individuals whom you are not emotionally close to (e.g. work colleagues) and, equally, feel emotionally close to individuals whom you do not interact with very often (e.g. immediate family or very close friends who live far away)."