Answer the following question given this paragraph: 

The organs of the GI tract are lined with mucous membranes that secrete digestive enzymes and absorb nutrients. The organs are also covered by layers of muscle that enable peristalsis. Peristalsis is an involuntary muscle contraction that moves rapidly along an organ like a wave (see Figure below ). You can watch an animation of peristalsis at this link: http://en. wikipedia. org/wiki/File:Peristalsis. gif .


Q: What is an involuntary muscle contraction that moves rapidly along an organ like a wave called?


A:
peristalsis