This question is for the people who have read the entire trilogy once a year since they were in middle school, or anyone with an absurdly detailed memory of events in the book.
When Frodo is talking to Galadriel in Lothlorien, she mentions that he has put the ring on “thrice” since he discovered what it was. Up to that point, I only count twice. Once, by accident (or the ring’s own design), in the Prancing Pony, and once on Weathertop. When was the third time?
I realize this is a completely insignificant question. It just bugged me. I’ve been rereading the book for the first time in fifteen years, and I’m relishing the details I had forgotten (particularly in the light of the movies, which are far more removed from the original text than I remembered).
In Tom Bombadil’s house, Tom puts the ring on but doesn’t disappear. Frodo gets suspicious that he’s been tricked, so when Tom gives it back, Frodo slips it on.
Near the end of chapter “In the House of Tom Bombadil” in FOTR.