Apologies in advance. This is a very specific question but its been bugging me and I don't know where else to ask the question. I've been listening to the complete Joe's Garage by Frank Zappa quite a bit lately. On the title song I could swear that I hear Mark Volman and Howard Kaylan (aka Flo and Eddie) singing backup. (e.g. starting at 1:45 the ay, ay, ay, aaaaa's and at 2:48 One, two, three, four, let's see if you've got some more). I don't see them credited and I know of course that the band with them in it never got back together after Zappa got thrown off the stage. I was wondering if they dropped by just for this song or if Zappa figured out some audio magic to use vocals from previous recordings. Given the subject of the song it would seem very appropriate.