"Box" is a poem by Michael Rosen, from his book "The Hypnotiser"
Disclaimer: This is a transcript of the video of Michael performing the poem, not the transcript from the book itself.
I made a box, with a lid, and locks, big enough for me to sit in. I took the chance, climbed in, and bolted the lid above me. I'd made the walls of my box, so that they could move in towards me. The sides and the top could come closer, and closer towards me, simply by my turning a handle from the inside of my box. Now that I was inside with the lid shut, I turned the handle and the box closed on me. I could feel the bolts in the walls digging into my skin. I could feel my neck being squashed down. I felt like clothes in a suitcase, my arms binding my body up. I stopped still, feeling the feeling of it. Look what I've made for myself. Look what I'm doing. Look at the box, though you wont see me. I'm on the inside. Walnut in it's shell.