In some remote village of india, one masterji is teaching the
mahabharat katha to a class. he is at the 'krishnajanma' part of
it. so let him continue instead of me

masterji : to bachcho, so kansa heard the akashwani that his
sister's 8th child is goin to kill him. he was furious. he
ordered
to put vasudev n devki behind the bars.first son is born, and
kansa kills him by poisoning second one is born n kansa thorws
him
off the mountain peak third one is born..

now Ramu who is smartest of the lot puts up his hand

masterji (sounding nervous n confused) : Ramu bete, whole india
does not have doubt in mahabharata n how come u have one?
Ramu Beta : masterji, if kansa knew that devaki's 8th child was
goin to kill him, why the hell did he put vasudev n devaki in
same
cell????????

U know guys, I must admit, I never got this doubt in my head
ever.... :)