Leaves of Mimosa pudica are sensitive. When touched the stimulus reaches the base of the leaf and the water in the vacuoles of the cells of the leaf loses water to the adjacent cell. All the water escapes the leaf which then becomes flaccid. This causes the leaves to close.

Why does touch-me-not plant close at night?

The leaves of the 'touch-me-not' fold up and droop each evening before reopening at dawn. They also do this more rapidly if they are touched or shaken. ... Many plants close up at night, usually to protect pollen or reduce water loss while the leaves aren't photosynthesising.

Why do Tickle Me plants close?

The closing of leaflets and lowering of the stalks can occur like a wave, with one stalk drooping down onto another, causing the entire TickleMe Plant to fold down. The TickleMe Plant moves in response to being tickled because of the loss of turgor pressure in the leaflets.