twitch

The most common forms involve abnormal eye movement, head-movements or movements in any other commonly used muscle. Some subtle forms also exist (and people don´t even realize they have it) like shaking the legs rhytmically under the table, playing with objects like pencils, pens, etc.

Animals also exhibit some peculiar forms of twitches, like the bulls, who make a characteristic leg movement when they´re ready to charge.

A very interesting book that can provide some (indirect) insight on the subject is ¨The Naked Ape¨ by Desmond Morris -- A good read, even if you don´t have twitches.

Twitch (?), v. t. [imp. & p. p. Twitched (?); p. pr. & vb. n. Twitching.] [OE. twicchen, fr. (doubtful) AS. twiccian; akin to AS. angeltwicca a worm used for bait, literally, a hook twitcher, LG. twikken to tweak, G. zwicken. Cf. Tweak.]

To pull with a sudden jerk; to pluck with a short, quick motion; to snatch; as, to twitch one by the sleeve; to twitch a thing out of another's hand; to twitch off clusters of grapes.

Thrice they twitched the diamond in her ear. Pope.

© Webster 1913.

Twitch, n.

1.

The act of twitching; a pull with a jerk; a short, sudden, quick pull; as, a twitch by the sleeve.

2.

A short, spastic contraction of the fibers or muscles; a simple muscular contraction; as, convulsive twitches; a twitch in the side.

3. Far.

A stick with a hole in one end through which passes a loop, which can be drawn tightly over the upper lip or an ear of a horse. By twisting the stick the compression is made sufficiently painful to keep the animal quiet during a slight surgical operation.

J. H. Walsh.

© Webster 1913.