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 a health of 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.