An animal's health is the amount of damage it can take before it is downed (dies or is tranquilized). In Carnivores 2 and Carnivores Ice Age, the health of animals and the power of weapons, both of which are set in _RES.TXT, have a one-to-one equivalence, meaning that, for instance, an animal with a health of 10 must be shot five times by a weapon with a power of 2 to be downed. Furthermore, if the "Aggression" option is set above 128 (if the slider on the Options menu is farther to the right than dead-center), the animal's health is modified by multiplying by the "Aggression" value and dividing the resulting total by 128: This is shown in the following line in Characters.cpp:
cptr->Health = DinoInfo[cptr->CType].Health0; if (OptAgres>128) cptr->Health= (cptr->Health*OptAgres)/128;
Thus, if the "Aggression" value is maxed out at 255 (by moving the slider all the way to the right), the previously mentioned animal with health of 10 instead has its health doubled to 20 () and requires ten shots instead of five to be downed by the previously mentioned weapon with a power of 2.
If an animal's health is set to 0 in _RES.TXT, that animal will immediately die upon starting a hunt. On the other hand, there doesn't seem to be a maximum health; while the value 1024 is used for this purpose, the animals with that health (Tyrannosaurus and Brachiosaurus) can both be downed as normal if shot enough times, and their health is increased as expected by a high "Aggression" setting.
The maximum amount of damage that can be done in a single hunt without debug mode (by selecting all weapons and, in Carnivores 2 and Ice Age, using Double Ammo) is 23.8 in Carnivores and 372 in Carnivores 2 and Carnivores Ice Age; notably, these are far short of the 1024 required to down the Tyrannosaurus without hitting its eye, or the Brachiosaurus.