User:Santa/Smokie killed Eko because it thought it was playing Wii (theory)
From Lostpedia
If the scene where the smoke monster kills Eko is examined carefully, it is obvious that the smoke monster has assumed the shape of a hand, and further that it is attempting to use Eko as a wireless inertial motion detecting game controller. However the game it was attempting to play is still unknown, and like the real Wii, Eko's straps were insufficient or nonexistent, and he was accidentally thrown to his death.
