All rodents have a pair of upper and a pair of lower teeth called incisors. Unlike our teeth, these incisors don't have roots, and they never stop growing! If they didn't gnaw constantly to wear them down, a rodent's teeth would grow until they pierced the opposite jaw.

When a female mouse gets pregnant, it only takes between 19 and 21 days for her to give birth to a litter, and she can get pregnant again 24 hours after giving birth. At this rate, if she doesn't waste any time, she can have up to 15 litters in one year.

The capybara (Hydrochoerus hydrochaeris) is a giant rodent native to South America. With an average weight of around 50 kilograms (110 lb), these barrel-shaped mammals are certainly no field mice. The largest on record was a 91 kg (201 lb) wild female from Brazil.

Each quill has a greasy coating that contains an antibiotic material. This protects the porcupine from developing infections when it accidentally sticks itself.

Perhaps the most distinctive feature of the beaver is its flat, scaly tail, which acts as a rudder when swimming and maneuvering underwater. If a beaver feels threatened, it will slap its tail on the surface of the water to warn other beavers in the area. Contrary to popular belief, beavers do not use their tails to pack or carry mud.

Mice have voracious appetites. They eat around 15 to 20 times per day. In fact, if food is scarce, mice will even eat each other.

Don't try to get rid of a rat by flushing it down the toilet--they can hold their breath for a long time and tread water for as long as three days.

The only species of porcupine that lives in the United States, the North American porcupine (Erethizon dorsatum) is the largest of all porcupines and can have more than 30,000 quills on its body.

Kangaroo rats obtain enough water from the metabolic oxidation of the seeds they eat to survive and don't need to drink water at all.

Castoreum is a yellowish exudate from the castor sacs of mature beavers. It is secreted as a brown slime that's about the consistency of molasses and smells like musky vanilla. Although it is no longer widely used in vanilla extract, it is still an FDA-approved natural flavoring.