Multiple choice general knowledge science & technology Lock Jaw, i.e., difficulty in opening the mouth is a symptom of Cholera Plague Tetanus Diphtheria Reveal answer Fill a bubble to check yourself C Correct answer Explanation Lockjaw (trismus) is a characteristic symptom of tetanus, caused by the toxin Clostridium tetani. This toxin causes severe muscle spasms and stiffness, particularly in the jaw muscles (hence 'lockjaw') and neck.