It's the line "Peter, I worried about you so" that really tears me up. Here Shadow is limping and having gone through an incredible ordeal and he's the one who was worried (I know, Peter was worried about Shadow too but still...)
Shadow's speech about why dogs attach themselves to humans:
Shadow: ...I shouldn't have made her come. Chance: It's not your fault, she wanted to come. Shadow: But it's my responsibility. I had a responsibility to Sassy, to love her and protect her. The same as I have to you... and to Peter. And the same as you have to Jamie. Chance: But we didn't ask for this job. Shadow: We didn't have to. It's built in. Has been ever since the dawn of time, when a few wild dogs took it upon themselves to watch over man — to bark when he's in danger, to run and play with him when he's happy, to nuzzle him when he's lonely. That's why they call us man's best friend.
It is a well-known fact that it is impossible for anyone who has ever loved a golden retriever to watch this movie without crying.
Not just a golden retriever, but any breed of dog.
Call it shmaltz and glurge all you want, but I dare anyone to watch the scenes with the little girl lost in the mountains without shedding at least one tear, especially when she and her parents are reunited.
When Sassy is reunited with Chance and Shadow. *
At the end when the kids and Bob are playing basketball and they call him 'dad'. This troper watched the movie all throughout her childhood, but it wasn't until I was 12 I understood that little scene. That LOOK Bob gets on his face when Peter says: "Yeah, come on, dad."