Here is my answer, I typed it in a document because I didn't want to have a long answer here, picture below. I hope I helped! :-)
Answer:
There is within me (and with sadness I have watched it in others) a knot of cruelty borne by the stream of love, much as our blood sometimes bears the seed of our destruction, and at times I was mean to Doodle.
Explanation:
This was probably one of the saddest lines in the entire story. He is older when he says this thinking back on the memories of him and his brother.
