The inclusion of the joker, making the deck 53 cards deep, is common is draw poker. Sometimes the joker is considered a wild card which can represent anything the holder desires; sometimes (as with legal games in California) it's limited to use as an ace or to complete a straight or flush. In any case, it's a powerful card. Ask yourself why an opponent would want to expose a joker while betting. There's something wrong, isn't there? He must be attempting to trick you into thinking he's strong when he's weak. This is probably a bluff.
