[Fordim Hedgethistle]

I think that there is a wonderful symmetry to the fact that Hobbits give away birthday presents rather than expect to accumulate them, for it emphasises what is at the heart of this chapter: Bilbo's struggle to give away the "birthday present" that he acquired from Gollum. There's a whole series of really wonderful contrasts that get set up in this: Gollum would never have given away his birthday present but kept it for himself; Bilbo, because he's a hobbit, does give away birthday presents, and does manage -- after a struggle -- to give away this one too.

Interestingly, just as Gollum lies about how he got his "birthday present" (it wasn't a real birthday present) so too did Bilbo lie about how he got the "birthday present". So the shadowy reflection of Hobbit and Gollum begins here with Bilbo: Bilbo is leaving far more than the Ring and Bag End to Frodo, but he's also bequeathing his shadowy (anti-)double Gollum to him as well.

In this way the whole of hobbit society is held up beside the core struggle around the Ring: can one give it up? The 'normal' way to be is to expect to get things on one's birthday (to celebrate yourself) -- the Ring demands a different kind of response, one which the hobbits are uniquely prepared for: to give of and from the self, rather than acquire for the self.