What is hidden in the picture?

While carpenters were working outside the old house I had just bought, I busied myself with indoor cleaning. I had just finished washing the floor when one of the workmen asked to use the bathroom.

With dismay I looked from his muddy boots to my newly scrubbed floors. “Just a minute,” I said, thinking of a quick solution. “I’ll put down newspapers.”

“That’s all right, lady,” he responded. “I’m already trained.”