Full Idea
The factors that determine exactly what you are doing when you produce a physical gesture include the customs, habits and conventions that are in force, so it is unlikely that anyone could produce correct behavioural definitions of mental terms.
Gist of Idea
Behaviour is determined by society as well as mental states
Source
Jaegwon Kim (Philosophy of Mind [1996], p. 36)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.36
A Reaction
This problem can be added to the problem that it is hard to specify behaviour without reference to mentalistic terms. The point is clearly right, as what I am doing when I wave my hand in the air will depend on all sorts of conventions and expectations.