When a thermometer is placed in a beaker of hot water, why does the mercury level drop, rise?

Question

The mercury expands when heated and that forces it from the bulb at the base of the thermometer higher into the capillary.

But Why does the mercury Drop First , then rise?

If the water is rather hot, the bulb of the thermometer expands somewhat (before the heat is transferred to the mercury) so the level of the mercury drops.