Two muscles are required to move a bone in the body what happens inside muscles when they contract

When you flex your muscles you are contracting them. When your muscle fibers gain tension through Actin and Myosin crossbridge cycling they may shorten due to the tension. This is called muscle contraction

The penis goes in the vagina kid, the 31 year old girlfriend must be your mom asking you are you ready to go to bed.

This gel or liquid can be placed under the tongue of an unconscious person. this is important because you should never pour anything down the throat of an unconscious person-- s/he could choke.