h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When I've played it, there has been one more rule: if a player puts down two cards, then all subsequent players MUST put down (or claim) AT LEAST two of their cards. If a player puts down three, then all subsequent players must place at least three, etc. This buildup resets every time the highest card is put down--if you are playing kings high, then once the kings are played the next player may place just one ace, no matter how many kings were played.

This has the effect of forcing players to lie in situations where it is blatantly obvious they are doing so--for instance, if you have 4 sixes and a seven in your hand, then by playing all four sixes you know the next player MUST by lying when he or she claims "4 sevens". Unless it's a two-pack game, of course.

Of course, you can also inflate the round through the usual methods of putting down the wrong cards for what you say they are--claiming three fives when one is a seven suddenly has an entirely new ramification beyond just ditching the extra card.