So I'm over on Facebook and I happen across a reference to lace fronts. So I do a bit of googling because, although I know these are wigs, I've never actually seen one...or had I?
Check out this slice of WTF from www.hairconspiracyextensions.com:
As remarkable as the technology is, these wigs are not without their imperfections. The attachment can be visible to the eye and can come unattached due to sweat or highly expressive facial movements. Just raising one's eyebrows can cause the "line of demarcation" to show because the glue can be stiff and does not move with the skin on ones forehead.
h/t Bougie Applebum