[quote=Automaton]
I have a question, are the plants just hostile in general?. Or are they like Some predators where once they eat they don't need to eat for a certain amount of time?. Or do they feed on the usual stuff (water,sun etc) and they kill humans just cause?.
[/quote]

Well plants need nitrates to live, when they became infected they lost the ability to gather nitrates from the soil, so they constantly catch and kill and digest animals to keep growing. The animals however only eat until they are full and stop until they are hungry again, they dont keep grow forever so they don't need a lot of nitrates.