After playing, a player must replenish his hand to eight cards. The player can take the top card from the deck or from the top of any of the discard piles on the board.

Yes, those discarded cards can be picked up by either player. That's why it's so important to carefully consider which cards to place there!

And if that's not enough to keep you on your toes, the hand ends when the last card is drawn from the deck. Do you keep drawing from there hoping to get that one card you need? Each draw brings the hand closer to an end!