What was the meaning behind the comic? What did he mean when he said he felt like there was a "5000 pound mouse breathing down his neck"? What did...

He felt that he would never again be free of the image of
himself as a "mouse"-- a Jew-- this literary device that he had created to convey his
parents' predicament as Polish Jews caught in the Holocaust. More than this, he felt
that he would never again be free to do work that was not, in some way, connected to
MAUS and his fame as the person who created this hybrid
tale/tail.

He has said he didn't want to be another Elie
Wiesel (writer about the Holocaust, who was actually a Holocaust victim himself). He
realized he had nibbled his way into a Maus hole...