Enabled sv_cheats 1, mat_wireframe 1 and also slowed down with demoui. Appears to be some pre-fire and well as player tracing.
Made a list of times to watch in each demo for better review.

cow.dem - start around 00:27.
cow2.dem - start around 00:10.
cow3.dem - start around 00:55.
cow4.dem - start around 01:15.
cow7.dem - start around 00:15.