The Wicked Willow of Withywindle

[Inziladun]

I'm reading through LOTR for the ?th time, and it's a testament to these works, in my opinion, that I'm always finding new things to ponder upon each reading.
I've been thinking lately about Old Man Willow. Not necessarily his nature, because I'm pretty well convinced he's a Huorn. What I'm wondering is this: what were his intentions when he trapped Merry and Pippin (and attempted to do the same to Frodo and Sam)?

[Frodo and Sam] went round to the other side of the tree, and then Sam understood the click that he had heard. Pippin had vanished. The crack by which he had laid himself had closed altogether, so that not a chink could be seen, Merry was trapped: another crack had closed about his waist; his legs lay outside, but the rest of him was inside a dark opening, the edges of which gripped like a pair of pincers.

LOTR The Old Forest

Later, Tom suggests the Willow had done that to Hobbits before.

'Old Grey Willow-man, he's a mighty singer; and its hard for little folk to escape his cunning mazes.'

LOTR In the House of Tom Bombadil

So what was the Willow after? If he had simply wanted to kill the Hobbits (as he threatened to do when Sam lit a fire against him), why didn't he do it straight away? Was he going to eat them? Ents and Huorns don't seem to be carnivorous. Did the Ring play a factor? Was the Willow obeying some other will in trying to hinder the Hobbits?