The animals made of thread are theoritically doable in any 3D package sw : these are just connected sticks.

To do that however, he probably used the original model of an animal and made intersections with planes, ... yet you can still do that (painfully) in meshmixer.

You can use a black/white drawing of a paw, export it to inkscape, save it as dxf after vectorization and import it in a 3D cad software to extrude it or make a pocket of it. Pretty simple. Basic sw should be able to do it if it can use dxf inputs.