Look, when you press the key of a piano, something fundamental happens. The key is actually a wooden lever, a bit like a seesaw but much longer at one end than at the other. When you press down on a key, the opposite end of the lever (hidden inside the case) jumps up in the air, forcing a small felt-covered hammer to press against the piano strings, making a musical note.
At the same time, at the extreme end of the lever behind the hammer, another mechanical part called a damper is also forced up into the air. When you release the key, the hammer and the damper fall back down again. The damper sits on top of the string, stops it vibrating, and brings the note rapidly to an end.
The extended and descriptive analogy of Chaplin as a piano is worth mentioning for three reasons. By playing him:-
1) there's is no jumping in the air at the extreme end of play
2) there is always a releasing of the opposition key. And...
3) in essence, his purpose is that of the felt covered hammer.
