The character wins the loyalty of an animal, provided that the character's heart is true. The spell functions only if the character actually wishes to be the animal's friend. If the character is not willing to treat the animal as a friend (for example, the character intends to eat it, or to use it to set off traps), the spell fails. An animal's loyalty, once gained, is natural (not magical) and lasting.
Number47 said:Respectfully, I disagree. A druid can only have so many hit dice of animal companions. Even though the friendship is instantaneous, real and pemanent, an animal will leave if the hit die cap is gone over. Similar for the ring. Remove it and its hit die cap goes from 12 to zero. Otherwise, everyone in the party will wind up with 12 hit die familiars by passing the ring around.
Speaks With Stone said:I don't believe that 2 rings of Animal Friendship would stack like that. Each ring allows you the ability to have 12 HD of animals befriended. Wearing 2 of these rings should not stack, they would be redundant, much like wearing 2 rings of resist fire provides no additional benefit over wearing just one.