Q:  8.6.17  3:59 pm 8.5.17  3:21 pm RE: RE: bilabial trill and oven display: I've never met anyone else who can do this! I try to explain it to people but they can't seem to do it. They probably don't believe me that it's real.  This happens because some lights flicker with the AC power at 50 or 60 Hz, and some of the segments are out of phase with the others. So if you vibrate your head up and down at about the same frequency, you see some lights appear to be higher or lower than others, depending whether your head is at the top or bottom of its vibration when that light flickers.  I find it works best with LED Christmas lights, but oven displays are pretty good too.