the vampire bats' habit of sucking an animals' blood is aided by a sucbtance that stops the blood from clotting と the vampire bat's habit of sucking an animal's blood is aided by a sucbtance that stops the blood from clotting はどう違いますか？説明が難しい場合は、例文を教えて下さい。

Both ways are possessive - bats’/bat’s and animals’/animal’s. But the first is possessive on a plural noun and the latter is possessive on a singular noun.

Bats’ habit means the habits of several bats (plural). A/the Bat’s habit means the habit of one bat (singular).

Animals’ blood is the possessive of animals and animals (plural) blood is the possessive of animal (singular).