Among the mammals that occur indoors it is only the true rodents, mice and rats, which attack timber. They can, however, cause a lot of damage, but much of this can be avoided if metal plates are fixed at the base of each outside door. Rats and mice always start to gnaw timber at an edge or in a corner where their teeth can get a grip. The size of the hole and the tooth marks will sometimes serve as clues to identify which species has been at work