On the song "EvenFlo" (and others), Jeff Ament does this thing that sounds like a pinched harmonic played near the headstock, and then he slides up, making it sound like a pinched harmonic slide. I've never been able to figure out how he does this... He usually does it right before the chorus. Is it a fretless bass with some kind of cool effects? Does he use some type of slide on his bass strings? I saw a guy do it in Guitar Center once, but I was talking to a sales person and didn't want to interrupt him. So what is this cool little sound effect?