But suddenly, without any warning, the dog jerked so violently that Thomas nearly dropped the leash.

— Hey, easy, what’s wrong with you? — he muttered, struggling to keep his balance.

Rex seemed to go mad: he growled deeply, from his chest, with a sound Thomas had never heard from him before. Then he lunged sharply toward the trash containers beside a dark fence. Snow sprayed out from under his paws; the dog was relentless, tense, as if something invisible were pulling him in.