Why Grover smell any monsters at the Thrill Ride even though it is a trap?

It seems like you're asking about the monster-hunting character Grover from the Percy Jackson series. However, there's no mention of a "Thrill Ride" in the books or movies. Could you please provide more context or clarify the scenario you're referring to?

Perhaps you're thinking of a different story or a specific scene. Let me know and I can help you understand why Grover might not be able to smell monsters in that situation.