https://en.wikipedia.org/wiki/Wah-wah_pedal
I'm going out on a limb asking for this to be added as an instrument, but on "Sinking" (track 13 of Beauty in the Backseat), Ken Sharp is credited as playing "wah-wah guitar," which suggests use of a wah-wah pedal. (I credited it using a custom credit for "effects" since he is also credited with playing regular "electric guitar" on that track.)