Learning PYRO in Houdini is not an easy task. Unlike the SOP, it is established based on the real physic model. For a better understanding of how PYRO works, We have to know what is behind the scene.
Recently I faced a problem when I was playing with the parenting of Geometry node in Houdini. I thought it wouldn't be a big deal at the beginning. However, the contents behind this node are much more than I expected.