Any ideas why docs put the thermometer under your tongue?

Oral thermometer. Placing the thermometer under your tongue will give a more accurate reading of body temperature as merely placing it in your mouth, especially with mouth open will be affected more by external ambient air.
To take ur temp. To get an accurate reading of your body temperature, the thermometer can be placed in your ear, in your mouth, under your armpit, or in your rectum. Each will give a slightly different reading. The mouth is easy and non-invasive.