The body is trying to warm up in the cold, and there is one good way for that - shivering. That is, frequent convulsive muscle contractions occur throughout the body, as a result of which we "shake up our body, forcing our muscle tissue to produce energy. That is, shivering is a defense mechanism against the cold of your body.
When your body temperature drops, your body tries to warm itself up. To do this, he begins to move his muscles. Hence the knock. It's actually the same when you're shaking from the cold. The body tries to warm itself up by moving the muscles.