[onoble]

This usually means he is not happy with what he thinks you are about to do...

If you had just grabbed chips and looked like you were thinking about calling then he is talking to induce a fold.

If you were about to pitch your cards then he is talking to induce a call.

In my experience though people who are bluffing and the villain is in the middle, rarely talk, they are usually too scared to talk.

Absent a specific read this is usually (but not always) a sign of strength.