Tics are repeated spasms or contractions of particular muscles, such as the muscles of the face (facial tic). A person who has a tic usually cannot control it, except for short periods.
Repeated clearing of the throat, sniffing, excessive blinking, and shrugging the shoulders are examples of tics.
Tics are associated with certain diseases, particularly Tourette's disorder. The cause is often unknown. Tics can also be brought on by medicines. Tics may become worse during periods of stress.