Good luck trying to find a specific thread of discussion in a 1000 page thread. My memory is hazy, but it wasn't so much a lengthy discussion so as much as Scalenex making a salient point and everyone agreeing with him. If Sarumon can corrupt birds and beasts, then Sauron can. A mouse is as corruptible as anything and probably will put less resistance than a hobbit. You try finding an evil mouse that has the power of invisibility.