A puff will give you a lift (I believe the technical term is velocity lift), as your apparent wind moves aft faster than your boat will accellerate. As you accelerate, the apparent wind moderates.

When the puff dissipates, the effect is a header. As you slow, the apparent wind will move aft.

If you sail into a hole, in theory, the telltales will show a header, until you bleed enough speed such that they point straight down.

How you react coming in and out of puffs has a lot to do with the strength of the puff relative to the true wind, position on the course, etc.

Speed & Smarts had an issue on this a whole back.

Hope this helps.

Mike