The tremor or involuntary quivering of your clutch foot (when you are driving stick ) and you just had a near-miss of an accident or you are being pulled off by a cop and you have drugs in your trunk or on your person. It is coursed by fear.
Druggie 1: Calm down man, you will get us busted
Driver druggie: I am calm!
Druggie 1: Oh yeah? then why is your leg bouncing up and down? You are scared man! you have clutch foot syndrome!