Rat teeth are harder than iron and platinum with a rating of 5.5 on the Mohs hardness scale. Rats are also very resilient, able to withstand greater falls, longer swims, and living on less food and water than humans. Rats also breed prolifically and without discrimination, requiring separation of parents and siblings to prevent inbreeding. Rats come in various species with the brown rat being most common, and can occasionally grow quite large, like the 15 pound Gambian pouched rat. Rats also carry and transmit numerous diseases dangerous to humans due to their proximity.