What is a mortise insert?

A Mortise is usually a piece cut out and the insert is called a tenon...these two pieces make a joint.

tenon

Lateral aspect of mastoid process and anterior half of superior nuchal line Lateral aspect of mastoid process and anterior half of superior nuchal line

well if you click to insert "keyframe" then you'll get a copy of the last frame you were on. say you had a flower, if you chose to "insert keyframe" on the next frame then you'd get another picture...