Question

Laboratory thermometer is used to measure the temperature of all things, except the human body. Why can't it be used for humans?

Answer 1

   The clinical thermometer that we use at home for measuring our body temperature, contains a kink in the tube containing mercury.  So the thermometer can be held in any direction or inclination or orientation (upside down or horizontal).  When the temperature is to be read, the thermometer can be held in any orientation, as mercury does not flow back into its tank.

   Clinical thermometer does not have any kink in the tube.  It is held upright while measuring the temperature and while reading the temperature.  So this cannot be used conveniently to measure body temperature.