Cat Truth #102: Blankets and Sheets = Invisibility

Cat love to burrow under blankets and sheets. I don't know what happens at your house, but when I attempt to make the bed here (which is a rare occurrence in itself), my cats don't vacate the top of the mattress. They don't even mind if I make the bed on top of them -- they just lie there and wind up looking like a mattress lump, changing the entire topography of the bed's top. And they act like they're not there. Blankets and sheets automatically make them invisible.