This is a test of commonsense. Complete the next sentence:

How to tell the difference between twins
Observe their facial features.
Twins often have different shaped eyes, jawlines, cheekbones, lips and other facial features, including moles or birthmarks on the opposite sides of their bodies that can help you tell them apart. You might also notice that one has a darker skin tone or complexion.
Look closely at how their height differs. You may discover that one twin is taller than the other, or tends to stand up a little straighter than his or her sibling.