Some behaviors, like humming, tapping, or word repetition serve as methods of self-stimulation, yet can come off as rude if you don't understand it.
If you’ve ever found yourself biting your nails, shaking your leg, or twirling your hair when you were nervous, then you can relate to the calming effect of self-stimulation. In people with ADHD, this sort of self-stimulating behavior — called “stimming” — may help them self-soothe or focus.
These self-stimulating behaviors may also help regulate hyperactivity or improve cognitive control, which is supported by the findings from a small 2015 study.