Yeah, in case it hasn't been clarified just yet, he gets a lot of squeals not only from typical pinch harmonics with vibrato, but also while the tremelo is way down hitting a natural harmonic (often on the more obscure frets...2nd, 4th, and in between frets) then almost simultaneously bringing the tremelo up to the desired pitch, and thus a wailing scream. And yes, some of the "step on a cat" screams are only fretted notes played normally while stomping on a Whammy pedal set 2 octaves up..."Becoming" being the most recognizable example.