The behind the scenes of Rain shows just how many effects shots they animated, and just how laborious the process was: https://www.youtube.com/watch?v=_GYwru8RdGQ

They also break the 4th wall specifically by showing the animator's point of view in a really fun sequence at the end of Puppets, and it's just... such a treat: https://www.youtube.com/watch?v=yhvVl0CW670