What is hidden in 3D image?

A college teacher reminds her class of tomorrow's final exam. 'Now class, I won't tolerate any excuses for you not being here tomorrow. I might consider a nuclear attack or a serious personal injury, illness, or a death in your immediate family, but that's it, no other excuses whatsoever!' 

A smart-ass student in the back of the room raised his hand and asked, 'What would you say if tomorrow I said I was suffering from complete and utter sexual exhaustion?'
The entire class is reduced to laughter and snickering. When silence was restored, the teacher smiled knowingly at the student, shook her head and sweetly said, 'Well, I guess you'd have to write the exam with your other hand.'