Riff question...

I was listening to this song by a band I really like and I keep wondering how they are playing the main riff. Are they using a slider maybe. I love the sound the get but I don't know how they are getting it.

http://www.youtube.com/watch?v=wmhfx_J0pZY

From about 00:30 to 00:45

sounds like a porbly dropped tuning arpeggiating chords in the beginning followed by some sliding but just finger slkiding like in Chop Suey