Is that Kim doing backing vocals on Seethrough Playmate?
 

Answers on the back of a postcard please

I pretty sure that's just Thurston double tracked like most of the rest of the songs on that album. Albeit singing it differently to the 'main' track and possibly through some sort of effect like a light distortion.

I could be wrong tho.

i used to think kim sang screaming skull. thurston can definitely pull her off. (and she's not on s/t p.m)