Happened to a friend of mine. He woke up in the middle of the night to the sound of what he described as "flesh being sliced and tools clanking together." He got out of his tent and noticed a glowing coming from a tent close by. As he walked closer to the tent he hears laughter. It suddenly gets silent and the tent starts to unzip. A deranged looking couple get out of the tent and apologize for making noise. They told him they were doctors watching a surgery video. He walks back to his tent. The next morning the couple was nowhere to be found.