My experience with snakes is all out of date; haven't kept them for almost 20 years. Back in the day, my "power-feeding" buddies always used rats if a snake were big enough to eat them, because it was easier to keep the snakes stuffed to the gills that way; an adult rat is at least 10 or more times the weight of an adult mouse. If you tried to get the same amount of bulk into a snake by feeding mice, the snake would often lost interest after the first 5 or 6 and stop feeding; whereas when you offered a rat, once he starts it he will finish it.
Just my opinion, not stating it as a proven fact...but I am convinced that snakes grow faster on rats just because they are eating more, not because rats are better on a "per-pound" basis. Growing at max speed doesn't equate with being healthiest, either.
I can't believe that people are still using Beef Heart to feed fish; I was reading about the negative aspects of this 30 years ago. Not at all natural, or what the fish have evolved to utilize.
I had a Red-tail Cat way back when who managed to ingest suction cups, odd rocks, plastic plant pieces; it became a challenge to "child-proof" his aquarium to protect him from his own appetite. I wonder...maybe I should have just included those items in his diet as "treats"...?