Table talk: If your teammate hasn't noticed a potential sequence and begins to place his chip in the wrong space, mum's the word.
You'll have the distinct disadvantage of playing each turn with fewer cards than your opponents - for the remainder of the game. If you forget to do so before the next player completes his turn, then you'll forfeit the right to draw a card. This allows you to draw a replacement card and play your turn as usual. You now have a dead card, which you can announce as such and discard at the beginning of your turn. For example, the cards in your hand include an eight of hearts, but when you look for the corresponding spaces on the board, you realize they're both already occupied by another player's chips. This occurs when you hold a card that can't be played on the board.
After you've done so, you may encounter a dead card.