Read this excerpt from Extremely Loud and Incredibly Close.

I started inventing things, and then I couldn’t stop, like beavers, which I know about. People think they cut down trees so they can build dams, but in reality it’s because their teeth never stop growing, and if they didn’t constantly file them down by cutting through all of those trees, their teeth would start to grow into their own faces, which would kill them. That’s how my brain was.

Which line best reflects the ambiguity of this excerpt?
I started inventing things, and then I couldn’t stop, like beavers
People think they cut down trees so they can build dams
in reality it’s because their teeth never stop growing
their teeth would start to grow into their own faces