Scars perpendicular to the normal lines of tension of the skin are more likely to stretch and to become more visible than scars that run along the natural lines.
The movements of facial expression may enhance this effect. Scars that are perpendicular to the "crow's feet" are extra conspicuous during a full smile. Horizontal scars crossing the frowning wrinkles are extra visible during frowning.
A W-plasty is performed by removing a fine saw-toothed pattern (like a series of w's) of skin together with the scar tissue. The resulting zigzag line is more conspicuous for some months because of its temporary pink colour. Once the colour has normalised, the scar becomes less conspicuous than before and it follows and bends to facial expression more fluently.