Answer: He´s wearing a pig mask to hide the fact that he´s a mouse (Jew)
Explanation:
Maus is a graphic novel about the Holocaust that depicts Jews as mice, Germans as cats, and Poles as pigs.
Vladek boards a train to Sosnowiec, despite not having the required paperwork. He wears a pig mask to pretend he´s ethnically Polish so he can be more sympathetic to the Polish conductor and get his help sneaking over the border.
