Emulsify is a fancy word for mixing two liquids that don’t want to combine, such as oil and vinegar. While you’ll never get them to blend into each other, you can break them down into tiny bubbles that will approach a thorough combination. Whisking very well does this, as does shaking the liquids thoroughly in a jar. A bit of mustard in a dressing helps keep the tiny bubbles in suspension and from breaking apart. If you want a well-mixed vinaigrette on your vegetables, mix it just before dressing, since it will break apart over time.