Garlic, like some other bulbs like tulips requires vernalization to grow. It needs a period of cold. If you are planting it, you would normally plant it in the fall if you are in an area with winter, if not, like tulips, you have to get it cold for a while to trick it. Forty degrees (about the temp of the fridge for a few weeks usually is enough to get it into growing mode again . If your garlic was shipped refrigerated, or was refrigerated in the store, it may already have several weeks of cold behind it and it's all ready to sprout.