This is a spike. Deadly to the touch, too.
This is a tricky spike. Not only do they kill on impact, but they also move towards you.
This is an "eejit" spike. Even though they are unpleasant to touch, they have very random movements, and so are easy to avoid.
This is a Pacman spike. They got their name because their movements represent the movements of the ghosts in Pacman.
Left: Fan, right, button. ʏou will get sliced to pieces by the fan if you don't stop it by using the button first.