Some pitchers will change their movements slightly, depending on the pitch that they are sending. The body seems to setup differently - ever so slightly, when say a curve, slider or off-speed is pitched. Now not every pitcher does this, at least not noticeably. Also, in latter innings, or with high pitch counts, fatigue starts to set in and the body can move in ways that shifts stress to other parts of the body. I’ve seen where the legs usually tip off fatigue - not big I might add, but they do. Release points are another sign of fatigue as are head movements.
Good question - shows observation skills.