However, if White chooses to decline the gambit pawn, there is this even faster trap:
Note that if White does not take the Queen, he is still in a rather bad shape as he must deal with the checkmate threat and his hanging Bishop. Be3 is what's needed, but after Bxe3 fxe3 Qh4+ g3 Nxg3, things are still very hairy for White.
After 1. d4 Nf6 2. c4 e5, White will usually accept the gambit pawn, so this trap is most likely to get most use:
Note that White still can't take the Bishop even after exchanging Knights, as this game from one of our group members shows: