There is a method pingpong. It is similar to a loop.
For example, animate the origami heart beats. If you try to shoot using a loop, first you animate the heart shrinks, then shoot to the point where the heart expands to its original shape, but the you can not erase the creases.
In this case, animate until the heart shrinks, and connects the reverse of the animation that the heart shrinks to the back. You repeat playback and reverse play, It is seem the heart to beat.
It is the beat animation.
It is also useful when you want to play loops but you can not restore them back to their original form, such as a destroys clay. In this way, the method of shooting only one-way animation and connecting the part returning to the original position by reverse play is called ping-pong.