Short answers, pulled from the story.
Rodents are a group of mammals in the order Rodentia, defined by a single pair of continuously growing incisors in each of the upper and lower jaws. They make up about 40 percent of all mammal species and use their sharp incisors to gnaw food, dig burrows, and defend themselves.
Rodent incisors grow continuously, so the animal must keep wearing them down or they will reach and pierce the skull. Enamel covers only the front of each incisor, and as the softer dentine behind it wears away, the tooth keeps a self-sharpening chisel-like edge.
The capybara is the largest living rodent and can reach 66 kilograms, though most rodent species weigh less than 100 grams. The largest rodent ever known was Josephoartigasia monesi, a pacarana that may have reached 3 meters in length and 1000 kilograms, living 4 to 2 million years ago.
Rodents inhabit every continent except Antarctica and have adapted to nearly every terrestrial habitat, from cold tundra under snow to hot deserts. They are the only terrestrial placental mammals to have colonized Australia and New Guinea without human help, and people later spread them to remote oceanic islands.
Humans have eaten at least 89 species of rodent, and guinea pigs were the main source of meat for the Inca Empire by 1500 B.C. In research, the house mouse is the most common laboratory rodent, and guinea pigs helped identify the cause of tuberculosis in 1882 and were the site of the discovery of vitamin C in 1907.
A small number of rodent species, chiefly rats and mice, cause most agricultural damage; in 2003, crops lost to rats in Asia were estimated to be enough to feed 200 million people. The black rat and its fleas spread Yersinia pestis, the bacterium responsible for bubonic plague, and rodents also caused the extinction of over 40 percent of Lord Howe Island's land birds after arriving in 1918.