I think that animalism or pet play is fascinating because there are different elements to it, which I think are well-reflected in the posts. The dynamic between each dom and sub is different, depending on how they view the exercise (if in fact it is an exercise as opposed to a full-time arrangement.) Some are excited by the sheer humiliation of it, the sub being limited to walking on all fours, barking, eating out of a dish and the like. Others focus on the meaning of the humiliation, which is the total submission of the sub in order to unconditionally please his/her dom. In stories, pet play is often used to break teh spirit of an unwilling participant - the once proud woman forced to pee on the ground and lap water out of a bowl, a humiliation that pushes her over the edge into eternal servitude.
For some it is a solemn, serious exchange, for others it is merely an hour-long diversion filled with giggling. As with most other things in the bdsm world, there is no right or wrong approach - it simply comes down to what works for the participants.
I agree with the camp who acknowledges the inherent limitations involved with pet play. I think it works best as a reinforcer between a dom and sub, where the dom can get pleasure out of his ability to control his sub and the sub can get pleasure out of pleasing her dom.