[Aquinasfan]

"Because no other species of animal can experience joy."

Thats absurd. You have never seen puppies or otters playing or colts frolicking on a sunny day?

Animals operate on instinct. They don't have will. Animal play is part of their instinctive behavior, and a sign of animal health or "contentment."

This differs radically from human joy:

joy ( P ) Pronunciation Key (joi) n.

1) Intense and especially ecstatic or exultant happiness. The expression or manifestation of such feeling.
2)A source or an object of pleasure or satisfaction: their only child, their pride and joy.

I think we tend to anthropomorphize animals. I know, I used to have a couple of dogs.

[monday]

"Animal play is part of their instinctive behavior, and a sign of animal health or "contentment."

It's the same with human children, or are you going to try to tell me that running, screaming, kids are deep in thoughtful contemplation of the joys of being 5 years old?

If I look back on my life, my highest highs and lowest lows were when I was young, before I learned reason and self restraint. I am not buying that it takes some higher intellect to experience intense joy.