I had the unfortunate experience to work at ValleyDale Foods for 6 months. Meat processors. Made bacon, hot dogs, "deli ham", etc.
Hot dogs are made with "chicken paste": measured by the pound, shoveled into a hopper and dumped in the mixer. Gooey yellow paste that came in drums. Anything from a chicken went into it.
We had macerators that had a series of sharp blades on two counter-rotating parallel rollers, followed by another set turned 90 degrees. Anything that went in was turned into meat paste. Prep for canned ham.
Hot dogs also got "boneless beef hearts", "beef salivary glands", and a few other cow parts that I forget. Packed in 30 pound boxes, frozen.
Still don't eat hot dogs!!