picking lint
I was playing this kid and he started picking lint. Afraid I rattled him so badly it became a lifelong obsession with the lint.
More seriously, any changes can be a sign of cracking other than striding to the table more confidently or starting to glide around the table. Talking more or less, tension around the eyes or them starting to dart, jerky movements, on and on. Conversely a purposeful stride and a clean confident looking set up and stroke can rattle your opponent when you are doing poorly and feeling sunk. I have turned games and sets around simply by my body language. It can be a tool to use or it can work against you. Shoulders straight, chest out, chin up, there is a reason soldiers are trained to look like that.
Hu