I can think of three books that have had this effect on me.
1. Slaughterhouse Five: I was reading it very soon after my Uncle Stu had died. When I got to the part where the guy describes feeding the dog the steak with bits of metal in it, I just started sobbing uncontrollably. It was that one image that let out all the grief i had been holding in for my uncle.
2. The Kitchen God’s Wife: This book is basically a biography that Amy Tan wrote about her own mother. This woman was married to an awful man and there is one scene wherein Amy Tan describes a fight between this man and her mother. Their little girl starts crying and finally the man stops yelling at his wife and goes over to the little girl. Instead of comforting her, he just starts beating her. When I read this, I burst into hysterical sobbing and ran into my mom’s room who had read the book and suggested it to me.
3. The True Confessions of Charlotte Doyle: The second time I read this book, I couldn’t remember why i liked it so much, only that I liked it a lot. I went along enjoying it, but I didn’t encounter that which had moved me so until the very end. Charlotte sneaks out of her house and goes back to the ship she spent the entire summer on and becomes a sailor with the slave she had previously looked down upon. When I read that part, once again, I burst into tears, but in a good away. :)