Red books.

True story:

"Genevieve, pick up this red cup and put it out in the kitchen."

. . .

Five minutes later.

"GENEVIEVE! I told you to pick up this red book and put it out in the kitchen. You moved from one side of the room to the other and didn't pick it up! And by 'book' I mean 'cup'!"

She picked up the cup and put it in the sink.