Ah, the beauty of seeing other people's cards even when they are grasping them tightly, glued, face down on the table. Two times in the last few weeks I have abandoned plots to raise in late position with junk to punish minimum raisers and limpers. Both times, warning bells have gone off in my head that UTG was trying to suck me into their AA net. After playing with the same group of guys for two years, it was as though big red, flashing lights were going off all around and the PA announcer was screaming "ACES, ACES, HE'S GOT ACES. HE WANTS YOU TO RAISE AS HE HAS ACES. SWEET, WONDERFUL ACES."
While playing on the defensive line in High School, I would recognize calls the opposing offensive linemen were making. Every team used the same ones. A crafty opponent would have known that I played offensive line as well and would have disguised their calls in an attempt to throw me off my mark. Against Irmo, I lined up on the inside shoulder of the tackle and heard the guard yell, "GEORGE," meaning he would kick out on me and the tackle would pull. Of course my first steps were into the chest of the guard, who I was able to throw to the ground before suprising the ball carrier who had been expecting a hole to appear. One bad word stalled a drive and contributed to the loss of the game.
In poker, you can often know other peoples calls. They are often the same as yours. Even if you haven't seen them before, they have been playing the same game, reading the same books, and watching the same programs. Until shown otherwise, it may be safest to assume transparency in their play.