A Hold cut at 0.5 s reads 3 just before and 0 at 0.5 s under 33.3 %,
133.33 % and 200 % stretch, and the frame matches the unstretched one.
A Birth Rate expression reading a Controller layer's Opacity before
0.5 s: changing the Controller changes the 0.9 s frame, and the cached
render matches the uncached one.