Let's explore the Fire Island Lighthouse

This beautiful old lighthouse is rumored to be haunted. While exploring, we find four fish fossils. 

One of these fossils has been cursed by Slick Sarah, Fire Island's famous ghost pirate. You must complete project #2 so you can figure out which fossil is cursed. This cursed object will help you decide which location to eliminate today.

Project #2: You will be using the sensor. This sensor detects cursed objects.

(Ok, in the STORY this sensor detects cursed objects... but in REALITY this sensor detects something else. What, you ask? We can't tell you! It'll ruin all the fun. You need to figure that out.)

Whichever object in the envelope reacts with the hall sensor is the cursed item. That item is the ??, this gives us a clue that we should elimiate the location of ??.