Deductive Reasoning
When Sokka walked into the room, Katara frowned when Aang quickly airbended a little further away from her and allowed some space between their sitting bodies. True, her brother had threatened a beating if Aang tied to get 'too close' but she was pretty sure he meant in a different sense than just how close they sat to each other.
"So, I've decided," the swords wielder said as he stood in front of the couple and stroked an invisible beard, "That you two do fit each other quite well."
Toph, who had been sitting with her feet propped up, asked with interest, "Really now? What tipped you off; how they're always smiling and goofing off with the other? How their heartbeats and body temperatures skyrocket whenever they're close to the other?"
"Yes; I've come to a very important conclusion," Sokka continued on, as if he hadn't heard the earthbender.
Aang unconsciously leaned a little forward, Katara just rolled her eyes and Toph lifted an eyebrow.
"For, I've discovered that you two work because Katara has enough hair to make up for Aang's total lack of it. If you're together, the hair ratio is balanced."
Aang fell accidentally fell off the couch, Katara sighed in non-surprise and Toph cackled.
"Our hair Sokka; really?" the waterbender master asked as she gave a hand for Aang to grab onto.
"Think about it," he said with gusto, "You have a crazy ocean amount of it and Aang is just…bald."
"I'm not bald, I shave it off," Aang said with a frown as he plopped back down on the cushions.
"Whatever old man," Sokka verbally and physically waved off; "Sometimes I forget how great a detective I am for figuring out phenomenons like this."
"Oh yes, you're deductive skills exceeds you," Toph quipped; "Only second to your drawing skills."
AN: Sokka's knowledge is like canon: UNQUESTIONABLE!