Yeah, proposition bets.
The one's your referring to are the one I thin Negreanu talked about in his blog awhile back.
Basically each player picked some numbers. If those three numbers are on the flop I win X amount of money.
For example, let's say that you picked 3, 4, & 7.
If the flop was 3/5/7 you net nothing.
If the flop was 3/4/7 you get X.
If the flop was 3/3/7 or 4/7/7 you still get X because it only had your numbers.
I think there's some bonus, like 10X, if the the flop is 3/3/3 or 4/4/4 or 7/7/7.
I'm probably messing it up, but that's the general idea.
When they played those during the big game, if you didn't declare your win you "slept" the prop and they don't have to pay you off, so it forces you to pay attention to
hands you aren't a part of. But during High Stakes Poker they couldn't really give the prop bets much attention as they'd interfere with the show. Hence, they wrote them down.
Eventually the producers found even that too distracting, and banned those prop bets.