Conan continues to investigate while playing dumb, but how does he give a deduction while being kept such a close eye on?

The waitress of Poirot Cafe, Azusa Enomoto, reported she received strange messages from a boy, suggesting he might be kidnapped or trapped in a location without food and water. The only way to find him is by reading his text messages. The boy only knows how to send, but does not know how receive. Conan must put the clues he gives to find out his location.