mimosa; sensitive plant
Refers to plants of the genus Mimosa, especially Mimosa pudica, known for folding its leaves when touched. The Japanese name literally means 'sleeping grass'.
The mimosa folds its leaves when touched.
Compound of 眠り (nemuri, 'sleep') + 草 (kusa, 'grass'), from the plant's habit of folding its leaves at night or when touched, resembling sleep.