There is a second page to the instructions, which says to press the flashing button which is supposed to say "develop." You either get the results or it says you made a mistake, sometimes just because you didn't open page 2 of the instructions.
The second time usually works, but you have to be careful not to spill anything.
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Show them to Mews then follow the instructions on the DNA test. After the x-ray tray is in the developer, press the flashing button to get the result.
You can only test two samples: the fur you bring back from your first trip to Puerto Rico, and the egg shells you bring back from New Jersey. Show these to Mews to start the DNA testing (follow the instructions, and even then you may have to do it twice).
Take the shells back to the Mews lab and test them. The DNA analyzer will prove the existence of the Jersey Devil.
You get the fur from a fence in Puerto Rico. Back at the lab, you run a DNA test, but it turns out to be ordinary coyote fur.
Since the monks won't let you test the Yeti scalp, you have no proof. Once you have the lantern and the footprint photo, you can find nothing at the Himalayas. However, once you prove the other three cryptids (Nessie, Chupacabra, and the Jersey Devil), Mews will send you in pursuit of the similar creature, Bigfoot.
You process the samples for DNA in the Lab, the left side of the Museum in the Mews mansion. (It is on the first floor to the right.) Follow the instructions to test samples, and show any photos to Mews.
The button flashes on the developer, but it is not labeled. Press it. When you select a sample from your item bag at the Mews lab, you follow the instructions on the DNA test. The final step is to place the x-ray screen into the developer and PRESS the flashing button. If you don't, it will never finish. When you do, the answer is instantaneous if you messed up. Otherwise, the test ends as "successful" and Mews will tell you the result.
21 students finished the test early. three fourths = 75% of the students
There are only 2 items you check with the DNA analyzer: the fur from Puerto Rico and the egg shells from New Jersey. If you follow the test process carefully (and press the devleop button on the developer), Mews will tell you the results.
On your first trip to Puerto Rico, drive the jeep to the house of the herder's brother (right side star). He says some fur on the fence is from the chupacabra. Take it back to run a DNA test, but it turns out to be from a wild dog.
You don't have to. After you get the fur from the fence in Puerto Rico and test it, you return there and the farmer is already setting a trap. All you need to do is use the jeep to corral 3 spotted goats into the clearing at Snaggletooth Rock (center star on the map). Then get out and join him.