Mellotronists

Hi folks.  My band is toying with "Dancing Days" from "Houses of the 
Holy" (somewhat to my chagrin, as I'm pushing for "The Rain Song") 
and I am having a really hard time determining what sort of keyboard 
sound the wanky-sounding little synthy part in the verses after the 
first chorus.  Anybody know what I'm talking about?  (Ever?)