That makes sense, but it’s you doing Herbert’s worldbuilding work for him. It’s not actually what the Rev Mother says. I’m suggesting that, as he wrote the book and serialised it, he had various ideas, some of which he then didn’t flesh out … my sense (as a jobbing writer myself) is: Herbert is opening one possible storyline here — there are lots of ways a SF writer might parse “animal”, including (I guess, if I start to think of it) Leto as one who has fathered this creature on Jessica etc. — but that he later changed his mind.