I was working on a new video for my series about this behavioral pattern:

For significant (mostly post-flop) bets or raises, when a player announces "Bet" or "Raise" and there's a significant pause between the announcement and putting in the actual bet/raise, it makes relaxation and a strong hand more likely and makes it unlikely the player is bluffing.

Here are a couple video examples with this kind of behavior in action:

Here's a hand from Pokerstars' The Big Game show, where Bill Perkins hits trips on the turn. The relevant action starts at 22 minutes:



Here's the most extreme example of this behavior I've ever seen. It's a pretty comical one. It's from the very first episode of High Stakes Poker. Relevant action starts at 31:30.



Other thoughts:
I don't think it's a super-strong pattern, as I could easily find you video examples of bluffers doing this, but I do believe it's a pretty reliable pattern, useful for when you're on the fence or for player-specific reads (where a player might often do this with strong hands).

Also, this behavior is often connected to other hesitation/uncertainty-type behaviors (like putting together chips for a call and then reaching for more chips, or having uncertain/unhappy facial expressions or postures), so it can be especially helpful if you're able to spot two or more behaviors that point toward the same meaning.

If anyone has any experience with this behavior or thoughts on the general pattern idea, love to hear from you.