Here's how it works:

* Expansion and Contraction: When the thermometer is exposed to a change in temperature, the liquid inside expands or contracts.

* Constriction's Role: The constriction, a narrow passage in the thermometer's stem, creates resistance to the flow of the liquid. This resistance slows down the expansion and contraction process, giving the liquid time to settle at the correct level corresponding to the actual temperature.

* Accurate Readings: Without the constriction, the liquid would move too quickly, making it difficult to get a precise reading. The constriction allows the liquid to stabilize, making the thermometer more accurate and reliable.

In simpler terms, the constriction acts like a "brake" for the liquid, ensuring a steady and accurate temperature reading.