If you asked Clumsy what Brainy reminds him of, he'd say this:
Brainy's like, like... a beehive? I ain't one fer fancy "metter-phors," but I know people, I know Brainy,an' I think that makes sense.
See, I know this, from years a' bein' 'is friend. On the outside, 'e's kinda mean, honestly. 'e's got a lot to say and a lot of it ain't nice, but it ain't 'is fault. It's kinda like the wild bees. They'll sting you, see, but it's in their nature. And they hurt themselves when they do it. I know how the others treat Brainy, an' really, it's Brainy's fault most of the time? So, Brainy's hurtin' 'imself too. But 'e's sweet inside, like the honey the bees keep. I love 'im, an' 'e loves me too, even if 'e ain't good at showin' it. I can tell. An' I wish the others would be a little bit nicer.
If you asked Brainy what Clumsy reminds him of, he'd say:
Clumsy's like a rock. He's as dumb as one of the rocks he collects, and don't tell him I said this, but he's as important to me as those weird yellow rocks are to humans. Human culture is so weird, I mean-
And then he'd go on a monologue about humans, facts picked up from books and mostly-wrong assumptions, and you'd zone out because he just wouldn't shut up.
They'd left Buddy behind, to be mauled or gruesomely eaten by Azrael. Brainy leaned against Clumsy, walking slowly and wincing in pain with each step. He was slowing them down, Brainy thought. And Clumsy had been having so much fun before Brainy's disappearance bothered him...
"You go on ahead, Clumsy." Brainy said. "I don't want to keep you from your friends."
Clumsy was not, in fact, bothered. He'd rather spend this one moment with Brainy than have eternity with the rest of his friends. He'd go to any lengths for Brainy, do anything to spend time with him.
"Oh, I don't wanna be with my friends, Brainy! I'd rather be with you!" Clumsy said happily.
Brainy was shocked. Why would anysmurf care about him? For all he knew, Clumsy was just hanging around with him out of guilt and pity. He felt like he was about to cry, but held back the tears threatening to spill.
"You- you would?" He stuttered out.
"Sure!" Clumsy responded. "I- I love ya, Brainy!" Oh, Brainy thought. Oh he... he loved him? They liked each other, they cared about each other, and in his heart he knew they loved each other, but they'd never said it out loud. It felt like some kind of declaration.
"I- I-" Loved him back? No, Brainy couldn't say that. He did, but he felt so much of it that he couldn't let anyone know. "I know how you feel, Clumsy. I know how you feel."
And that was enough. Clumsy understood.