Rivalry
It was a contest. A constant contest, a tug-o-war between them. How many times can you die? I bet I can out smart you! It irked Her no end, but the reassembly machine liked them, and she needed them, anyways. Still, hours wasted, lost, as they played their silly little games.
When they worked together, though…it was shocking the difference. Suddenly they'd go from two bumbling robots who's stupidity could rival the moron's to class-A testers, as fast and efficient as the human they'd replaced. Flashes of blue and orange would fly past Her cameras, followed by the soft ding as the test was completed.
…And then she'd check in on them, and Orange would be in Blue's disassembly pod, while its irate partner pointed at the other tube and glared. Again.
And that was how it usually was, in the tests. Take away a thing's fear of death, and what motive does it have to go faster? While they clearly didn't like pain, they worked and, more importantly, played straight through it. They could be clever, but preferred to use trial and error until they found the solution to the test. When She put them on time limits was when they did their best work, but they were so easily distracted… pausing to mock the turrets, or unable to resist a chance to knock their partner into the acid, but always arriving with a few milliseconds to spare. If She didn't check their memory logs, She'd have suspected them of doing it on purpose.
Like right now. They were standing in the middle of the test chamber, playing rock-paper-scissors until, it seemed, they both got three in a row at some point. Blue won, throwing its hands in the air and racing over to Her camera, waving excitedly.
"Yes, I see you. And no, I don't care."
It seemed to droop a little, until Orange came over and hugged it from behind. Blue squealed, and hopped back, tipping them both off balance, sending the two bots sprawling on their backs on the floor. She sighed. And it only took them two minutes to solve the chamber. You'd think they could make it to the lifts.
ATLAS and P-body are so much fun, with all their little goofing-off challenges. The multi-player mode is less of a cooperative testing initiative, and more of a how-many-ways-can-we-annoy-GLaDOS.