A motion path can be used to show a prop changing size.
1. Apply a motion path to a prop:
2. To show the prop getting larger, adjust the silhouette of the prop to make it bigger:
3. Then move the silhouette over the original prop:
4. When you preview the scene, the prop will appear to get larger.
The same steps apply to show the prop getting smaller. Adjust the silhouette of the prop to make it small and place it in front of the original prop. When previewing, the prop will appear to become smaller.