One fun fact about mayonnaise:
Technically, it's a stable emulsion, a mixture of two things that don't really want to mix at all -- oil and acid (lemon juice or vinegar) -- with something to keep them together, or emulsify them, once they meet (the lecithin contained in egg yolks). Commercially produced mayonnaise labeled as real must use only egg as the emulsifier, and by law must contain at least 65 percent oil. The salad dressing I like so much has no egg to keep the oil and acid together, but I still love it. Sometimes, though, only the real thing will do, so I always have it in my refrigerator.