How to make animation separate from mask?

Question

Video

Hello.
The bottom line is this: you need to animate the leg, like it sways, I put the mask so that it was like behind a chair (or whatever this clamshell is called), but the problem is that the leg moves along with the mask, how to make the mask motionless?

Answer 1

Select the chair leg on a separate layer and place it above the leg layer. If the chair moves, bind its position to the chair.
Toggle Switches Modes at the bottom of the timeline.
For the leg layer, select one of the Track Matte modes