Why does Julia quickly remove the thermometer from Ita's mouth and place the thermometer in her armpit?

Ita is delirious and very likely would bite down on the thermometer. The thermometer is glass and filled with mercury, so it could easily break. Julia says that many nurses had learned the hard way. When Ita began to wake up, Julia knows she has to quickly remove the thermometer from her mouth. As she still wanted to take Ita's temperature, she moves it to her armpit, knowing it would not be as accurate.