What's Inside a Rendering Truck?

Do you know what "rendering" is?

Rendering is the process that converts "waste animal tissue" (heads, legs, hoofs, fats, and bone) into both "edible" and inedible materials.

Right now, a truck is driving slaughtered animal's remains to a rendering plant where they take "edible fat materials" and heat them with steam then separate the fat from the bone with boiling water.
The final product that these animals have been reduced to will be used in human food products and pet foods.