clonus
n. a type of involuntary movement caused by a rapid succession of alternate muscular contractions and relaxations. Although some forms of clonus, such as hiccups, are considered normal, most such movements are abnormal; for example, clonus occurs as part of a tonic–clonic seizure. More severe forms are associated with spinal cord damage, poisoning (e.g., from strychnine), or an infection (e.g., syphilis).