I always get very wary when someone takes a long time to act after a scare card hits.. people think if they take a long time it will make us think they are unsure of their hand. Beware of the long pauses followed by a big bet/raise.

When people act fast they generally have air. Occasionally someone will insta check when they hit a set on the flop. On a dry board, I Cbet a bit less when someone does that insta check on the flop.

Taking a few extra seconds sometimes means second or third pair, or a draw they are calculating odds for.