No human has a perfectly symmetrical face. That would be weird. However, studies have shown that we're more likely to be attracted to people with symmetrical facial features.
Use the slider to see what it would look like if a celeb had a totally symmetrical face. Right is the symmetry of the right side of the celeb's face; left is the symmetry of the left side of the celeb's face. Leave the slider in the middle to see what the celeb actually looks like.