What is the use of kink near the bulb in clinical thermometer

Since, in clinical thermometer, mercury is used and level of mercury rises very rapidly with small variation in temperature that's why thermometers provided with kink near the bulb so it prevents the level of mercury from falling when taken out of mouth.

Hence, the answers are it prevent the level of the mercury from falling when taken out of the mouth, it allows the level of the mercury to fall when taken out of the mouth.