If you go by the actual definition of what defines an animal, it is literally impossible not to constantly harm animals. Either the rabbits caught in the threshers, the tiny organism we step on, the mites on our face we consume unknowingly.
Even the strictest Jainist can't stop from annihilating an uncountable number of tiny animals that live in, on and around us. (though to their credit, they sure do try).
Causing zero harm to animals is enough.
It's totally within reach, too. You just have to take responsibility and DO IT.