More from "Improbable Journeys"

I was minding my own business, serving up my dinner earlier, and two of the other characters from Improbable Journeys started a conversation in my head, so I wrote down the conversation, then expanded on it a bit. I'm not sure whereabouts it fits into the tale (quite near the beginning, though). I'm slightly concerned the character descriptions are over the top so I'd be grateful for some feedback.

"Is this him?" asked Castella, tapping the screen in front of her.
"That's him," confirmed Ash.
"Right. Let's go and see him then. And let's hope he's not too argumentative."
"He's a teenager. They're programmed to be argumentative," answered Ash.
"Programmed?" asked Castella, stopping dead so that he almost ran into her back. "You didn't tell me he wasn't human."
Ash sighed. "He is human. 100%. I meant genetically programmed."
"Oh. Why didn't you say so then?" She strode off.
Ash rolled his eyes, unseen, as he followed her down the corridor to their ship. Sometimes he really wished she wasn't quite so literal-minded. He hurried to catch up with her, knowing she would be irritated if he kept her waiting. They made an interesting contrast. Castella was a tall, red-haired woman, willowy in build, but strong, as all TICK Agents had to be. Ash was short, and looked even shorter next to Castella. He was also bald and tubby. For him, staying fit was a constant battle; not that he over-ate, it was simply that Nature had intended him to be a short, tubby man with a jolly face. He looked like a caricature of everyone's favourite bachelor uncle. Castella, on the other hand, was probably a caricature of everyone's least favourite spinster aunt. She had hawk-bright eyes and a beaky nose. Ash had often wondered if she'd ever considered surgery, but he'd always concluded that she would consider it mere vanity, and the one fault she definitely didn't possess was vanity.