To Twitch

1. (intransitive) To perform a twitch; spasm.
2. (transitive) To cause to twitch; spasm.
3. (transitive) To jerk sharply and briefly.
4. (obsolete) To exert oneself. [15th-17th c.]
5. (transitive) To spot or seek out a bird, especially a rare one.

Usage notes

When used of birdwatchers by ignorant outsiders, this term frequently carries a negative connotation.