"At several points during the filming of Twin Peaks, Lynch improvised by incorporating on-set accidents into the story. The most notable of these occurred when set decorator Frank Silva was accidentally filmed in a mirror during Sarah Palmer's vision at the end of the pilot. When David Lynch saw Silva's face, he liked it so much he kept it in the show, and cast Silva as "BOB", the mysterious tormentor of Laura Palmer."
Damn, that walked the line between cheesy and really creepy. Wasn't that the same dude who played the Antichrist Randall Flagg in that goddawful TV movie of The Stand?
This scene works a lot better in context. Particularly given the way the previous five minutes of all three of them singing that weird song completely throws you for a loop, and then this creeps you the fuck out.