They only hit the player when they're above a certain velocity, so the player can roll them around and use them for various things, like solving puzzles (think those Pokemon type puzzles where you have to move blocks to certain locations) or breaking blocks:
They can also kill enemies, which means the player will want to use them sometimes, but need to be careful not to hurt himself:
And they have a few extra uses, like walking on spikes:
. Like to play it.
