The various rejected cores GLaDOS considers using for her experiment before finally settling on Wheatley. These include an overly-polite core, a core that randomly screams for no reason, and a core that speaks badly-translated Japanese. ("Hello. The sandwich you have eaten is made of bacon. My great uncle goat buried his french fries in your underpants.")
The Running Gag of Wheatley exiting cars via the window and falling flat on his face.
GLaDOS's observations on human Wheatley's progress are full of these—particularly his experience with popcorn:
He had documented how the kernels were quite warm in his mouth. How the old maids (though Wheatley had no idea how anyone would know how the elderly taste like corn) were something not to be eaten but spat out. How annoying it was to get little bits of popcorn stuck in one's teeth (Wheatley made a mental note that a toothbrush and a hairbrush were not interchangeable).