crab and dolphin (big)
A dolphin is bigger than a crab.
whale and jellyfish (hard)
A whale is harder than a jellyfish.
starfish and octopus (fast)
An octopus is faster than a starfish.
shark and penguin (heavy)
A shark is heavier than a penguin.
eel and seahorse (thin)
An eel is thinner than a seahorse.