Science says some sea otters rarely use rocks while others use them for almost every meal, their teeth may explain why

Sea otters survive largely on marine invertebrates such as sea urchins, crabs, clams, mussels and snails. Getting to that food, however, isn't always easy. Many of these animals are protected by tough shells or hard exoskeletons that can withstand substantial force, leaving otters with the challenge of breaking through these natural defenses before they can eat.