Final answer:
A rectal thermometer is specifically designed for taking an infant's rectal temperature. It provides an accurate measure of core body temperature, which is different from using ear or infrared thermometers.
Step-by-step explanation:
The device used to take an infant's rectal temperature is a rectal thermometer. Unlike infrared ear thermometers, which perform rapid temperature measurements and are excellent for use in settings like an aircraft carrier's ventilation system as described in Figure 13.5, or the aural thermometer developed by Diatek Corporation and NASA for rapid measurement without contact with mucous membranes, a rectal thermometer is specifically designed for safe insertion into an infant's rectum to measure body temperature. It is important to use a rectal thermometer for this purpose as it provides a highly accurate measurement of core body temperature, which is critical when monitoring the health of an infant.