All spells that affect others, even animals, generally provoke an RR.
So if you used an "animal" spell to control a T-rex, or a Gigantic Spider, they're more likely to resist, but if they fail, you gain control over them.
Sort of like using "m" spells on the 1st level trainee, or the 20th level champion. . .as the reward goes up, the risks of failure go up.
As far as I understand the glossery at the start of SL, it essentially breaks living things into:
Animal: A living creature capable of feeling and voluntary motion, but excluding those characterized as beings.
Being: Any intelligent creature, including all humanoid types, enchanted creatures, etc. Intelligence should be characterized by system and/or Gamemaster.
So it doesn't matter if the animal can turn invisible and shoot lightninbolts out of it's head. . .if it's of the animal kingdom and not sentient, it's an animal. . .
So the large spider in CT is an animal, but the Giant spider is a being because it's listed as being intelligent.
Of course, there are few unintelligent creatures with special powers, but there are a few, like an electric eel is an animal even with it's shockbolt table zap attack.