Doubt In Mahabharat

In some remote village of India, one teacher is teaching the Mahabharat story to class 6 students. He is at the 'Krishnajanma' (Birth of Lord Krishna) part of it.

Teacher: "Kansa heard the Akashwani (prediction) that his sister's 8th child is going to kill him. He was furious. He ordered to put Devki (his sister) and Vasudev (her husband) behind the bars. First son is born, and Kansa kills him by poisoning...Second one is born and Kansa throws him off the mountain peak. Third one is born..."

Now Ramu, who is smartest of the lot, puts up his hand. "Sir, I have a doubt" (sounding nervous and confused).

"Ramu, the whole of India does not have doubt in Mahabharata then how come you have one?"

Ramu : "Sir, if Kansa knew that Devaki's 8th child was going to kill him, WHY THE HELL DID HE PUT VASUDEV AND DEVAKI IN THE SAME CELL?"