Horton's Worry is a phrase from the classic Dr. Seuss book, 'Horton Hears a Who!' In the story, Horton is an elephant who discovers a tiny speck of dust containing a whole city of microscopic creatures called Whos. He is determined to protect them from danger, despite the ridicule of his peers. The term 'Horton's Worry' refers to the anxiety he feels as he tries to keep the Whos safe. The crossword solution for this term is 'EGG, ' which is a reference to the fact that the Whos live on a small dust speck that looks like an EGG.