Bartleby's first appearance. Heck, most of the scenes involving Bartleby, especially when he's with Smiley.
Of particular note is Smiley's expression when he, Phoney, and Gran'ma Ben are backed up against a wall by a herd of Rat Creatures, with no hope of escape, and one of them sits up on his hind legs (exposing his uncropped ears) and tilts his head in recognition.
From Treasure Hunters:
Smiley: You know Bartleby, I never had a pal like you before.
Bartleby: Me either!
Bone making a quiche and giving it to the rat creatures in celebration of the Winter Solstice. "Peace on Earth, fellas!"
Anything Phoney did early on that showed that he really did care about Fone Bone and Smiley.
Phoney: You can blame me all you want, pal, but you watch your mouth when your talking about my cousins!
He also shows this later near the end, when Gran'ma Ben offers him a chance to go home via a shortcut tunnel. Phoney's response?
Phoney: I'm sorry, I... I can't leave without my cousins.
Then, when Phoney is arguing with Fone toward the end, when Fone wants to stay with Thorn but Phoney wants him to return to Boneville...
Smiley: Phonicible P. Bone, you are going to support your cousin no matter what decision he makes because you love him.
Phoney: ....(Sighs in resignation and acceptance.)
In spite of what Briar turned out to really be, there was something so sweet about gruff, grumpy Lucius talking about the girl he very nearly married.
Smiley: You ever been married?
Lucius: I almost got married once.
Lucius: It was a long time ago.... She was a beautiful woman... Th' most beautiful woman in th' whole valley.... (smiles) We were in love, and we courted, a lot of folks thought we were gonna get hitched....
Smiley: So what happened? Why didn't you get married?