A tic's a sudden, repetitive, nonrhythmic, stereotyped motor movement or vocalization involving discrete muscle groups. Tics can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and vocal tics are, respectively, eye blinking and throat clearing. Movements of other movement disorders (for example, chorea, dystonia, myoclonus) must be distinguished from tics. Other conditions like autism and stereotypic movement disorder also include movements which may be co… (More on Tic)