The subtitle, simply put, is a metaphorical statement that contextualizes the overall title within the historical events Spiegelman's graphic novel describes. To some extent, it could also be considered a form of hyperbole, but given the scale of bloodshed in the Holocaust, it is not really an exaggeration at all.
A metaphor is a literary device in which an idea is expressed figuratively rather than literally and in which a comparison is implied between seemingly unlike things. No one can literally "bleed history," of course. But the idea conveyed by Spiegelman is that the immense suffering of the Holocaust is like that of blood being poured out, and the essence of it is analogous to the historical process. The Holocaust is the focus of Maus, but "history" as a whole is an endless series of wars, mass murders, and atrocities. These are symbolized in the metaphorical reference to one's father's "bleeding."
The literary device on which Maus in its entirety is based is anthropomorphism , the...
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