This is the way it happened in the books:
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Jon says:
"He gives his sons to the wood."
A long silence. Then: "Yes." And "Yes," the raven muttered, strutting. "Yes, yes, yes"
"You knew?"
"Smallwood told me. Long ago. All the rangers know, though few will talk of it."
"Did my uncle know?"
"All the rangers," Mormont repeated. "You think I ought to stop him. Kill him if need be."
The Old Bear sighed. "Were it only that he wished to rid himself of some mouths, I'd gladly send Yoren or Conwys to collect the boys. We could raise them to the black and the Watch would be that much stronger. But the wildlings serve crueler gods than you or I. These boys are Craster's offerings. His prayers, if you will."
His wives must offer different prayers, Jon thought.
"How is it you came to know this?" the Old Bear asked him. "From one of Craster's wives?"
"Yes, my lord," Jon confessed. "I would sooner not tell you which. She was frightened and wanted help."
"The wide world is full of people wanting help, Jon. Would that some could find the courage to help themselves. Craster sprawls in his loft even now, stinking of wine and lost to sense. On his board below lies a sharp new axe. Were it me, I'd name it "Answered Prayer" and make an end."
Yes. Jon thought of Gilly. She and her sisters. They were nineteen, and Craster was one, but...
"Yet it would be an ill day for us if Craster died. Your uncle could tell you of the times Craster's Keep made the difference between life and death for our rangers."
"My father..." He hesitated.
"Go on Jon. Say what you would say."
"My father once told me that some men are not worth having," Jon finished. "A bannerman who is brutal or unjust dishonors his liege lord as well as himself."
"Craster is his own man. He has sworn no vows. Nor is he the subject to our laws. Your heart is noble, Jon, but learn a lesson here. We cannot set the world to rights. That is not our purpose. The Night's Watch has other wars to fight."
The book version definitely didn't say that the ranger's knew why Craster was sacrificing to the woods. But Gilly did give more specific hints than Mormont did. She told Jon:
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"The cold gods," she said. "The ones in the night. The white shadows."
And suddenly Jon was back in the Lord Commander's Tower again. A severed hand was climbing his calf and when he pried it off with the point of his longsword, it lay writhing, fingers opening and closing. The dead man rose to his feet, blue eyes shining in the gashed and swollen face. Ropes of torn flesh hung from the great wound in his belly, yet there was no blood.
"What color are their eyes?" he asked her.
"Blue. As bright as blue stars, and as cold."
She has seen them, he thought. Craster lied.
It's pretty clear that they were all surprised when the wight attacked Jon and Mormont in the Lord Commander's tower. So it seems most likely that they just thought Craster was killing the babies himself or the elements and animals were killing them as part of a sacrifice, rather than giving them to the Others.
Edited by Tadco26, 16 April 2012 - 03:31 PM.