Shrews typically live on land, feeding mostly on insects, but also other small food such as worms or seeds. Some are specialized for life in trees or underground, but most sniff around on the forest floor. Because shrews have high metabolic rates, even above what you'd expect for such a small animal, they eat nearly their own body weight in food every day. To get more nutrients and calories, they eat their own feces (refection). Their vision is poor, and they use their good senses of smell and hearing to find food. When they find moving prey, some shrews immobilize it with venom dispensed through grooves in their teeth. While a bite from a venomous shrew does not kill a human, it can cause painful inflammation, which explains why people are described as shrews if they are painfully ill-tempered. Shrew venom is potent and has possible medical applications, such as in the treatment of migraines.

Mammals have a unique arrangement of a lower jaw directly hinged to the skull. The upper jaw is fixed, while the lower jaw is movable. A powerful bite results which, coupled with specialized teeth, allows mammals to eat a diversity of foods. Straight-edged incisor teeth at the front of the jaw are for cutting and gnawing. Pointed, canine teeth on the sides can grab and tear meat. Flat, broad molars are used to grind or crush plants or shelled animals. Mammals tend to have more than one type of tooth (heterodont dentition), with the mix depending on diet. Meat-eaters have sharp incisors and canines plus slicing molars; mammals who eat tough plants have duller incisors and canines, but large, ridged molars. All types of mammal teeth are replaced once or never during a mammal's lifetime. A coating of enamel, the hardest material found in a mammal's body, makes teeth built to last.