[andyfox]

You should act on what you believe happened. That is, if he intended to call, and then changed his mind, you should call a string raise. If you feel he intended to raise, you should allow it.

The guys who are angling by watching their opponent's reaction usually have enough chips in their hand to raise and then decide to either call or raise depending on their read of their opponent. I can't recall a guy putting out only enough chips to call and then saying raise as an angle before going back for the additional chips.