Thomas's devil horns

The other day, we put Thomas down for a nap. He did not fall asleep right away. He spent his usual time up in his crib talking for a few minutes. Then we heard him cry, but we assumed it was because he was really tired and just needed to fall asleep.  However, when we went to get him up from his nap, we noticed he had two red bumps on his forehead, from where he had bumped it on the crib slats. They looked like little horns, especially when he'd smile mischievously.  We know he's a sweetheart though.