Pretty neat what he's done with the flash thing. I take issue with the Zep tune though.
Forward:
Yes there are two paths you can go by, but in the long run, there's still time to change the road you're on.
Backwards:
My sweet Satan, there was a middle path, would make me sad, which now I am, Satan.
Also elsewhere in Stairway you can hear:
Sweet Sally awaits me.
and very very clearly you can hear:
I wish it would snow.
The snow thing is uncanny and by far the most clear phrase in the whole song.
In the end though, all this is just coincidental sounds that our brains make words out of. I went to a Christian school coming up and we were filled with this backwards masking "evidence", and I spent hours looking for stuff. I had a reel to reel tape machine back then, so it was easy for me to experiment with it. Trust me, it's just as easy to find demonic messages in backwards sermons, or backwards anything for that matter.
It's lots of fun though!