Due to temperature differences between the bottle and the environment, your screen can fog up.  It should recede after leaving it in equilibrium temperature for a few minutes.  We also placed water absorption stickers inside Gululu to ensure safe operation of our electronic parts.  

*Please also note that the bottle can only take a maximum temperature of 40 degrees Celsius and 104 degrees Fahrenheit.  Putting overly hot water into your Gululu bottle can cause the screen to fog up as well.