Definitions of jerk:

• noun:   an abrupt spasmodic movement
• noun:   a dull stupid fatuous person
• noun:   (mechanics) the rate of change of velocity
• noun:   a sudden abrupt pull
• verb:   throw or toss with a quick motion

  Example: "Jerk his head"

• verb:   move with abrupt, seemingly uncontrolled motions

  Example: "The patient's legs were jerkings"

• verb:   make an uncontrolled, short, jerky motion
• verb:   pull, or move with a sudden movement

  Example: "He turned the handle and jerked the door open"

• verb:   jump vertically, with legs stiff and back arched