Most refrigerators have a light that goes on when the door is opened. Turning on a light is classified as a havarah. Even though one does not intend to turn on the light when opening the door,1 this is prohibited2 since there is a direct reaction which will definitely take place. The easiest way to avoid this problem is to unscrew the lightbulb before Shabbos or Yom Tov. If one accidentally opens the refrigerator door (without unscrewing the lightbulb) and turns on the light, they may not close the door as this would be turning off the light.
Religion brings peace to your life and sours your milk.