Jo Beth's right arm started doing things on its own while she
slept.  It would bend at the elbow, raise that elbow high over
her head, and then reach with her right hand way down her
back.  Jo Beth would wake during the night in pain from that
unnatural pose.  She'd straighten out the arm, only to wake
again with her right hand again halfway down her back.

Her own arm wasn't in her own control.  
An Arm's Homage to Kubrick

Where Jo Beth's arm honors high humor.
Study Questions:
Is there anyone who doesn't love Dr.
Strangelove?
Was Jo Beth's left arm just lazy?