A barber generally keeps on snipping the scissors in between the actual cuts. There is a particular phrase for this behavior. I have come across this phrase before, but can't recollect it now. The phrase was a generic term for such involuntary acts and the barber's one was a good example for it. The closest I can some up with now is "fidgeting", but I don't think that was the word. Two close phrases I came across today are "muscle memory" and "automaticity"
Tics, perhaps? (This is often part of 'nervous tics', though not all tics are nervous ones.)
It sounds like a complex motor tic.
(Edited to clarify "nervous" and link to definition.)