Atsushi Yasuoka posted a progression of a T. rex from skeleton through musculature to final render, built in Blender, Maya and Ziva VFX. Guillermo del Toro replied: “Beautiful jiggle—”.
Two words, and they identify precisely the thing that is difficult.
Why jiggle is the hard part
Creature animation has a hierarchy of difficulty that is not obvious from the outside.
Primary motion — the skeleton moving, the gait, the weight shift — is animation. It is hard in the craft sense and it is well understood, with decades of technique behind it.
Secondary motion is what the flesh does because the skeleton moved. Muscle bulging under contraction, fat sliding over muscle, skin lagging and settling, the wobble that continues for a few frames after the limb stops. It is not animated; it is a consequence, and it is almost impossible to key by hand convincingly because the brain knows exactly what mass behaves like.
And it is the single strongest cue for weight. A creature can have perfect primary animation and read as weightless if the flesh does not respond. Conversely, a slightly imperfect walk with correct secondary motion reads as a real animal. Our perception of how heavy something is comes almost entirely from how its soft tissue lags behind its bones.
Which is why del Toro — a director whose entire career is built on practical creature effects, animatronics and prosthetics, where the flesh is literally latex and foam with real mass — went straight to the jiggle. That is the criterion a practical-effects person judges a digital creature by.
The anatomical pipeline
Building outward from the skeleton is the approach, and it is worth understanding as a method rather than as a flourish.
The conventional route to a creature is sculpt the outside — model the surface you want, then rig it with a skeleton and skin weights, and fix the deformation problems as they appear. Fast, art-directable, and it produces creatures whose anatomy is implied rather than present. When they deform badly you adjust weights, which is treating a symptom.
The anatomical route builds the skeleton, attaches muscles with origins and insertions, layers fat and fascia, and puts skin over the top. The surface is then an emergent result of the structure underneath. When the leg bends, the muscle shortens and bulges because it is a volume-preserving soft body attached at two points that have moved closer together.
Ziva VFX is the tool for this — a soft-tissue simulation system using the finite element method, with materials for muscle, fat, skin and cloth, and constraints for attachments and sliding. It is the lineage that produced the creature work in most recent large-budget features.
The cost is enormous and the payoff is specific. An anatomical setup takes vastly longer to build than a weighted skin, needs simulation time per shot rather than evaluating in real time, and is much harder to art-direct — you cannot simply move a vertex. What you get is deformation that is right in every pose, including poses nobody tested, and secondary motion for free.
The three-layer thing worth knowing
If you are approaching soft-tissue simulation for the first time, the layer that gets skipped is the one that matters most.
Muscle is the obvious layer, and it is where beginners put all their effort. It contracts, it bulges, and it is attached to bone.
Skin is the obvious outer layer.
Fat and fascia between them is the layer that produces jiggle, and it is the one people leave out. Fat is a low-stiffness, high-damping volume that slides over muscle rather than being bonded to it. That sliding is what creates the lag, the wobble, and the settle. A muscle-and-skin setup with no fat layer produces deformation that is correct and reads as rubbery — tightly coupled, no overshoot, no delay.
Get the fat layer in and the creature acquires mass.
Posting the progression is the smart part
Yasuoka showed the progression — skeleton, then muscle, then flesh, then render — rather than only the finished image.
That is why it got noticed, and it is a lesson for anyone sharing technical work. A final render of a T. rex is one of ten thousand online and is judged against photographs of things that do not exist. A progression demonstrates the method, is legible to other practitioners, and invites exactly the kind of specific technical response del Toro gave.
We have made this observation twice in a fortnight — about the Marvel Rivals art team’s pipeline breakdown and Karlis Stigis publishing his space-colonization setup. The work that travels in this field is the work that shows how.