Literally.

As I started off this morning, about 30 seconds into my ride I remembered that the front disc had been noisy enough on the last ride that I wondered if the wheel was in straight. So I came to a gradual stop on the 14% downhill that starts my ride. As I went to open the quick release, I accidentally touched the rotor with my thumb and it burned me. I mean, it burned me so quickly and intensely that I thought I had cut myself on something. It took a minute for me to realize what had actually happened.

I knew disc brakes got pretty hot, but I was shocked to see it heat up that much that quickly. Is this normal?