AGAIN.....A thermostat probe, for the most part should always go on the outside of the tank. Usually what you want to see is the probe either sandwiched between the bottom of the glass tank and the UTH or taped onto the UTH directly, but not on the inside of the enclosure. If your snake urates (pees) or spills water on the probe, the probe can sense a decrease in temperature and cause your UTH to spike in temperature, potentially burning your snake.