Our big tabby, Zoe, loves to get inside cardboard file boxes. She has a way of slithering under the lid and letting it settle back on top so you don't realize there's a cat inside. Quite a few times I've lifted a lid off an apparently empty box and been surprised to find her curled up inside. Zoe's much smaller sister, Kaylee, likes to sit on top of file boxes and amuse herself by clawing at the edge of the lids.
Tonight I was vaguely aware of Kaylee clawing away atop a pile of boxes behind me in my office. After about 20 minutes of the clawing sounds, I turned around and saw her just sitting there on top of the boxes, looking as innocent as possible: "Who, me?"
I went over and picked her up, and was startled to hear the clawing noises again, even though I was holding on to her. That's when I realized the clawing was Zoe, who'd been stuck inside the box for 20 minutes because Kaylee had been sitting on the lid, preventing her from getting out!
What's truly scary is that Kaylee had obviously been doing this on purpose.