What is the function of kink in a clinical thermometer?

Nickel thermometer provides an accurate range of temperature measurement from 35°C to 42°C. When the thermometer comes in contact with the patient's body, then the temperature expands out of the bulb. When it is pulled out that, the temperature goes back to normal and start to contract.

a kink in the glass tube of the thermometer breaks the Mercury as it contracts and stores the highest temperature reading and also maintains the accurate reading.