Better don't joke about this kind of things.
I have a distant relative, used to be into photography. This was in the film days.
One day during the 7th month he decided to go take photographs of people giving offerings, burning incense, etc.
According to relatives, during the photography session, he used alot of flash and adjusted the offerings to get a better shot.
Soon weird this started to happen. He was always complaining he could see "a head at the ceiling corner" staring at him.
Then one night he started screaming. His parents ran into his room. He was saying a "burnt man crawled through his window and went under his bed." There was nothing under his bed, but weird thing was, they could all smell a terrible stench in his room.
They took him for an exorcism and things became better, but everyone said he was never the same. His parents suspect he can still see things sometimes but they don't bother him as much as before.