Rusted Metal

That night he could not sleep. When he went to bed after brushing his teeth, he lay down with a book, this one titled "lost treasures". He finished a few chapters, placed it on the tabletop next to his bed and went under the sheets.
A few minutes later, when he was at the brink of losing his consciousness to blissful rest, his stomach started bubbling. He jumped out of his bed, surprised.
It kept on bubbling and got hotter every few seconds, until he could not bear it anymore and ran to the kitchen for some water to cool his burning insides.
When he reached the basin, however, his stomach was back to normal, and the house smelled peculiarly, of rusted metal.