When Monica and Chandler are at the craps table and are rolling the dice, there is a guy to Chandler's left with a yellow shirt with a pattern on it who appears to be mouthing Monica and Chandlers lines.
When Phoebe pretends to be a businesswoman interested in the blackjack dealer and Joey being hand twins, she uses the name "Regina Phalange". The phalanges are the bones that make up the fingers of the hand (and the toes of the foot).
The little boy who laughs at Rachel's mustache is A.J. Foster. Since it was his first time on a set, Kevin Bright hired his real life parents to walk behind him in the scene. After, Bright was so thrilled with his performance that he took AJ into the gift shop on the set and told him he could have anything he wanted. AJ chose a squirting slot machine toy.