How Philip get infected (my research)

[Astor]

I think I found out how he get infected:

Each time I played I saw something strange, I don't know how to explain...It's in that room with the barrel which you need to get burning to go on, next to it is that grid, there is something...I know it! It's a strange effect which is only a few seconds visible...that barrel that's the reason. Maybe he got infected while the barrel was burning...

Is something on that true, or am I the only who have saw that strange thing!?