Whilst I was a diligent physics student many moons ago I’m afraid my magneto-hydrodynamics at an event horizon is a bit ropy….
However, it is always interesting to see an analogue that demonstrates the physics more clearly than any equation!
Take a look at this story on the BBC News website: http://www.bbc.co.uk/news/world-us-canada-33282343
A great big vortex in a lake being drained to control flooding. What is REALLY interesting is the spontaneous generation of instabilities that propogate UPWARDS out of the vortex throat and against the flow. #4 right at the end is the best! Stretch the plughole analogy to curved space (that is imaging the ring of foamy water being a sphere) and what we might have at V404 is a smilar event. The “flooding” is accrection of new material and the flaring is instabilities of material flashing around the event horizon. I wonder how long before this will appear in a paper somewhere. What do you know!, it happens right here on Earth, just not so violently…… 😉