involuntary
adjective uk/ɪnˈvɒl.ən.tər.i/ us/ɪnˈvɑː.lən.ter.i/
非自愿的;不由自主的，无意识的
not done by choice; done unwillingly, or without the decision or intention of the person involved
A sharp tap on the knee usually causes an involuntary movement of the lower leg. 突然轻轻敲一下膝盖，小腿通常会不由自主地动一下。