>>17745843No, slobber just means it's tired and will attack less until it replenishes its energy. Tired monsters will try to recharge faster by going to another area to catch prey or feed on carrion, but you can attack them while they're eating for free hits.
The only real sign that a monster is close to death is if it starts limping to another area. That also means that it's ready to be captured.
Also, Plesioth is an asshole with broken hitboxes and nobody likes fighting it with melee weapons. Stupid hip check.