Full Idea
One must already understand what it means to ascribe to someone a belief that it is raining in order to be able to generate the items on the list of rain-behaviour, so the list cannot be used to explain what it means to ascribe to someone such a belief.
Gist of Idea
You can only identify behaviour by ascribing belief, so the behaviour can't explain the belief
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 3)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.43
A Reaction
This is thought by many to be a decisive objection of behaviourism, because it makes the enterprise hopelessly circular. If I put up an umbrella when it was dry, you would probably infer that I believed it was raining.