OP meant that "yes" is not a word in Spanish. The word "sí" is indeed the affirmative and it's used mostly the same as yes in English.

oh, I see now! that makes more sense when I reread it.

The comic strip character was acting all knowledgeable by quoting Shakespeare as saying "yes" when the character meant "sí", but misspelling Shakespeare's name as "Chespier", something like misspelling it "Shaespier" in English.