Calvin and Hobbes by Bill Watterson for August 13, 1993
Susie: This must be the coded letter Calvin's trying to get me to read. Hmph, not much of a code...just backward letters! I can read it through the back of the page. "Dear Hobbes, If Susie goes behind our house at noon, all our secret plans will be ruined. Calvin." Gosh, it's almost noon! I'd better hurry over to Calvin's house if I want to spoil his plans! Calvin: Wheee! Ha ha! She fell for it! C'mon Hobbes, hurry!