Hey, that's an idea, Miniver. I've been idly considering this as regards teleportation: how does the device know what to take and what not to? What if it disassembles, moves, and reassembles your atoms, but not your clothes? Things could get very awkward very quickly.

Which is the beauty of magic. It's not regulated to strictly scientific laws: in fact, but it's very nature, it bends or breaks those laws.

As Ajnos pointed out, you obviously have to be in direct contact with the ring for it to work. I don't know if it is significant, but Digory grabbed Jadis' heel, not the hem of her skirt, when he wanted to pull her back into the Wood between the Worlds. Jadis was astride Strawberry who, being a cab horse, would have had a virtually bare back; Frank had touched Strawberry, and Uncle Andrew (for reasons unknown) had taken Frank's hand. So they were all directly touching when Polly touched the ring.

I think Jenny's right but I thought up a new theory for fun.
What if, the rings have to do with whether something is animal, vegetable, or mineral (That would explain the bulldog's fascination.) Unless a mineral was in direct contact with a vegetable or animal it wouldn't come along. The paving stones wouldn't come because Strawberry would be wearing metal shoes.

Very clever of you to think of the horse's shoes, Hermit! I like having a theory that takes them into account. It has a delightful ingenuity to it--kind of like a Rube Goldberg machine.

I agree with Jenny. That is rather the beauty of magic and the supernatural is that it is not in the bounds of the natural laws.

I think it is significant that they had to be all touching just as the yellow ring had to be touching their skin to take them to the wood. When it worked as a magnet the first two times with Jadis she was first holding Polly's hair (Which I suppose counts) and then Digory's ear.

That is a neat theory Hermit

Here are some more random thoughts about the rings--

1. as to the forming of the rings from dust:
just as crystals form a distinct shape as they grow, perhaps the inherent crystalline shape of the special dust --when suspended in the proper medium-- was circular, resulting in ring-shaped crystals

Perhaps the different colored rings and their different properties (i.e., whether being attracted or repelled from the Wood between the worlds) came from differences in the suspension liquid that the dust was exposed to

2. the humming vibration coming from the rings suggest to me that they emitted some kind of wave frequency for which animate objects serve as conductors but other inanimate materials would act as insulators. When a connection was made with a conductor, the result would be the release of a magical force that would either draw those touching the rings (or part of the animate conducting chain) to the Wood between the Worlds, or away from it.

Here are some more random thoughts about the rings--

1. as to the forming of the rings from dust:
just as crystals form a distinct shape as they grow, perhaps the inherent crystalline shape of the special dust --when suspended in the proper medium-- was circular, resulting in ring-shaped crystals

Perhaps the different colored rings and their different properties (i.e., whether being attracted or repelled from the Wood between the worlds) came from differences in the suspension liquid that the dust was exposed to

2. the humming vibration coming from the rings suggest to me that they emitted some kind of wave frequency for which animate objects serve as conductors but other inanimate materials would act as insulators. When a connection was made with a conductor, the result would be the release of a magical force that would either draw those touching the rings (or part of the animate conducting chain) to the Wood between the Worlds, or away from it.

Interesting thoughts, Benisse! Fun to apply chemistry to Narnia. And why not? It's a material world too, though with some magical processes added to the mix.