If you'll forgive an ignorant question from an amateur: as Airbubba mentions up there, the pilots apparently didn't shut down engines until several minutes after they stopped in the mud (in the video they talk about that at about 4 minutes in, and the video starts only after the incident has happened and someone's run out to the fence with camera). Why would that be? I'd have thought that after the "oh sh*t" moment, since they weren't about to go anywhere under engine power, they'd have shut down right away, leaving only the APU running (or starting it) if they needed it, which they also talk about on the radio. Or might they have been sitting there thinking "maybe we can power back onto the concrete"?