Freak the Mighty Lies and Deceit Quotes

How we cite our quotes: (Chapter.Paragraph)

Quote #7

"I'm telling tales, my dear, not lies. Lies are mean things, and tales are meant to entertain." (15.16)

Seems like Grim might be splitting hairs here. Is a lie a lie, or are there variations?

Quote #8

"Tonight they'll take me down there for my special operation. The next time you see me, I'll be new and improved." (23.24)

Up until the end, Freak is 100% behind his lie. Why does he hold on so tightly to it?

Quote #9

"You couldn't lie to Kevin. I tried a little fib on him when he was about seven years old, because I didn't think a child could handle the whole truth, and you know what he did? He looked his disease up in a medical dictionary." (24.34)

We know for sure that Freak is capable of lying. Is that why it's not easy to trick him? Or is he just too smart for it?