You know that if you warm up your coffee in the microwave oven only the liquid inside gets hot while the ceramic cup or mug remains the same temperature. Well, I found that out the hard way when I did not know my husband already heated my cup of tea , so I drank a mouthful of hot liquid, thinking it was perfectly safe and cold. Yes, I know – it would have been better if I had been warned, but I hadn’t. But now, if you use this ingenious Heat changing Tardis mug you will know in an instant if the coffee or tea inside is hot or cold. That is because the mug changes depending on the temperature.