GLaDOS: You dropped this

"Don't pick it up. Just leave it in the corner, and I'll deal with it later."

Introducing Companion Cube-chan, trying to be helpful in returning a core GLaDOS seems to have dropped.

And I made a little side story for GLaDOS, which is that she created, or at least she believes to have created, the purple core before all the others. But after building one core to be her sort-of-gaurd-dog, one to help her in making cake (And in the end, ends up having her waste her allowance on an ungodly amount of rubarb products, including rubarb on fire) and one to entertain her, she finds the purple core to be a burden, a bother, and totally usless. She she often purposly tries losing track of it. But Companion Cube-chan always comes to save the day, and return what GLaDOS lost.