Re: C4D Liquid on Human Body

Yes, that's exactly what I had in mind. There's not a lot to it: I would render the body from a top view, with a close up on the area to be swabbed and use that as a reference in AE to draw the animated mask. Do an animation so you can follow the paintbrush thing in AE.

Then load the animated mask into the alpha of a texture, set the other channels to whatever you want to simulate the painted look, and then drop that material on the body object so it's tag is to the right of the existing tag. If you go to the viewport's Display menu and enable "stacked materials" you should see the result in the viewport. You'll also have to go the animated material's Editor tab and check the "Animate Preview" box.

The only caveat is that you'll have to play around with the alpha material's UV mapping to get it to match up. You can probably get away with Flat mapping (texture tag>Projection). Use the texture axis tool to rotate and scale the projection so it matches up.