What's Wrong with This Box?

My daughter dug through the recycling bin for a box to use for a fairy house. Later, as my husband was leaving for work I heard him telling her something on the front porch. She immediately came in and asked my backside (I was washing dishes), "Where can I find another box? Dad says I can't use this one!"
"Why not?" I asked turning around
She said, "I don't know!?" as she held up the large Tampax box I had thrown in the recycling bin the day before.

Thank God he saw it before she carried over to the neighbors house!