It's not an animal it's a medical instrument.
A thermometer.
Usually a vet or animal Dr. will insert a thermometer in the animal's rear end. .
By capturing it and using a thermometer.
use a thermometer.We can feel how hot or cold something is. However, sometimes things are just too hot or cold for us to feel safely. At other times we need to know exactly how hot or cold something is. When we need to measure temperature correctly we need to use an instrument called a thermometer. This measures temperature in degrees Celsius [sometimes called centigrade] or degrees Fahrenheit. There are different types of thermometers for different situations. A medical thermometer, for example, needs to be very accurate. It measures in fractions of degrees. When we are ill, even tiny changes in temperature are important. Some thermometers use a liquid that moves up a very fine glass tube. Most room thermometers, and outdoor thermometers are like this. The liquid is either mercury [ which is poisonous] or coloured alcohol. As liquids get warmer they expand [get bigger], and move up the tube. Water expands too, but not as much as alcohol and mercury. Thermometers that might be used by small children are not made of glass. They use a digital display which lights up the temperature. Inside the displays are chemicals that change colour according to the temperature.
Tree crickets, because temperature affects their rate of activity.
Celsius, Fahrenheit, and Kelvin.
Rectal thermometer is the only way that I know of.
thermometer and light meter.
Thermometer
a thermometer
With great difficulty, since the thermometer will probably too big and, regardless of the thermometer's size, the animal won't like it at all. You should take your guinea pig to a vet if you think it might be ill.
What kind of thermometer you use to measure the body temperature