This shot is my favourite out of the whole film because it was one of the more challenging, and most satisfying, animation-wise. The puppy design, by Scott Leberecht, had to be envisioned with the tools at the time, which was Meta-Clay balls in Softimage 3|D. If you had ever used that tool, you would understand what a task it was to get the right shape, and then rig it so it could be animated. I used reference from my own little puppy at the time to get the feeling for Flubber's transformation and canine acting. I will be uploading the wireframe version where I will be discussing the more technical aspects of this shot.
At the time, it was the densest CGI structure ever made. There were about three hundred Meta-Clay elements, all spine/spline/cluster controlled. It took about two minutes just to refresh to the next frame. It took me about two months to build and rig.
First of all, sorry for the quality: this was ripped from a DVD copy of a D-beta tape.
As you can see, there is a heck of a lot more going on that you would think for this shot. As you see at the beginning, there is the Blob Flubber sitting in the matchmove representation of Robin William's hand. Now keep in mind, back then, all of the matchmove stuff, both camera and object geometry, was HAND-ANIMATED. There was a crew of guys from the old practical ILM shop who transferred into the digital side: some of these guys worked on "Empire Strikes Back" and onwards, so they knew how cameras worked and were able to use this experience to do the one thing that made ILM stand out back then, properly reconstruct scene and camera information into the computer.
So we have the Blob sitting there, with what appears to be somesort of orthopedic back-brace and a black fuzzy alien sitting in its belly. Well, the "brace" is in fact the up-vector construct I had to develop because the Meta-Clay elements that made up the Blob Flubber where not spherical, they were shaped like overlapping mass of blobby M&Ms because when the client want to get away from the "pear-shaped" Flubber that spherical Meta-Clay created. BUT, Softimage3|D didn't have up-vector constraint and (of if it it, it did not work well at all) when they were lined up on the cluster-deformed path spline that held them in place, they would start flipping randomly along the shortest axis. This was bad because it looked like the Flubber was having a seizure when animated. So I had to invent an up-vector constraint that worked consistently. So that's what the "brace" is, which had to be, at times, key-framed to prevent the flipping.
So what's that alien? Why it's the Puppy Flubber rig, elements and geometry, all compressed, waiting for the moment Robin Williams sticks his fingers into the Blob Flubber. Presto-change-o, without any quick cutting or changing of the scene file because of the nature of Meta-Clay, the Puppy Flubber pops up, all ready and IK-rigged, and the Blob Flubber lines up inside the body part of the Puppy.