I have been testing the function both with animals and there are some that cause problems, for example with a wolf I tried to regenerate its tail, and it worked perfectly, but with the Husky it regenerates automatically. The only difference I noticed is that the Husky has 11 health in its tail while the wolf has 10. I also had the same problem with the wargo, which has 14 health in its tail. No errors popped up. After that, I tried to heal an insect queen by making it regenerate its left front leg, which has 196 health. When it regenerated (instantly), it died.