A rat's teeth never stop growing, which is why they gnaw on hard materials.

The longer version

Rodent incisors are open rooted, so the pulp at the base keeps adding material and the tooth erupts continuously. Only the front surface carries hard enamel, while the back is softer dentine that wears away more quickly.

That difference is what keeps the edge sharp: as the animal gnaws, the softer rear surface is ground down faster, leaving a thin chiselled blade of enamel standing proud. Without constant abrasion the teeth would curve, overgrow and prevent the mouth from closing properly, which is why gnawing on wood, seed husks and other hard materials is a routine part of rodent behaviour rather than a sign of damage. The jaw also moves in a precise forward-back grinding stroke.

Where this entry sits

This collection gathers small surprises about mammals, reptiles, amphibians, birds, fish, insects, and the pets living alongside people. Expect odd details about senses, anatomy, and everyday behaviour that many people never notice in the animals around them. The full list sits on the Animals page, where every entry is listed in order.