You Know THAT Part

Sometimes you read a book and there is THAT part, like the Red Wedding scene in A Storm of Swords and then you recommend or loan the book to somebody and you just can't wait until they get to that part.  I'm pretty sure this is how it goes down.

This is what happened with my poor Hubby when I forgot to warn him about a certain event involving a certain house elf in Harry Potter and the Deathly Hallows.  He still hasn't forgiven me :-)  Also for a great laugh watch the reactions to people who watched the Red Wedding on tv and have never read the book, ooh revenge is sweet for all those people give us a hard time about actually reading the book!

What books do you know have THAT part?  What is your favorite reaction of other people who have read it?  Do you spoil it for people, or let them walk into the terror/horror/intense sadness all on there own?