Gamasutra has a massive, eight page interview with Portal's Kim Swift and Erik Wolpaw. They talk about everything from the design decisions the team made, to the horrors of GameStop's used game pricing, and what other games the team enjoys playing.

I'm curious to know — this is also tangential — how did Mike Patton get involved with Portal?

EW: He does the zombie noises for Left 4 Dead, and he had recorded like a two-and-a-half minute demo for us. It wasn't like we were auditioning him. We just wanted to know what he would sound like. We had Ellen originally do the anger sphere, but she was just too nice, and couldn't quite pull it off.

I was panicking at the last minute, and just happened to be doing some of the Left 4 Dead stuff, listening to the Mike Patton voice, and I was like, "Oh, we should use this!" So then we had to go through a little bit of union stuff, and we were eventually able to buy it and put it into the game. I don't think he even knows.

KS: Yeah, he knows.

EW: Does he? Okay.

The full eight page interview goes off on some wild tangents at times, and every bit is worth reading.