I played in a new poker game last night.
I won, which is nice.
A "tell" is something you do inadvertently, even subconsciously, the tells other players (at least those paying attention) something about your hand. It's usually very subtle.
You might remember a MASH episode where everyone realizes that Major Winchester whistles when he's got nothing.
Well, here's a freebie, if we ever play poker: Pokerface in DC got a good hand last night and promptly spilled his beer all over himself.
That's a tell.