They are large black cleats with white shoelaces and spikes sticking out from the bottom.
Role in the episode
When SpongeBob and his so-called bodyguard, the Tattletale Strangler (whom SpongeBob hired because he was initially unaware of his true identity), attempt to gain entrance to the former's house, the latter suggests going through the top windows. The Strangler asks SpongeBob for assistance, which he agrees to offer and jumps on top of him, accidentally placing his spiky cleats in his eyes. This causes severe pain for SpongeBob's "bodyguard" and the process goes on for six hours. Afterwards, SpongeBob puts bandages on the Strangler's eyeballs and apologizes for the damage done, then proceeding to grab his spare key under the mat to unlock his door.