Panel One: Jon's pen is as long as a human forearm, and possibly, if no foreshortening is at work, longer.
Panel Two: I can put no price on the pregnant pause of this panel.
Panel Three: I can only assume Jon is writing a poem to Mystique to hand-deliver on opening day of X-Men 3. J/K you guys, LOL! The joke is that "wolverine" is inherently inappropriate to use in a romantic poem. I say "Not so!" and offer Jon a few rhyming words: latrine, sardine, spleen, benzene, vaccine, obscene, gangrene. J/K again! Those are all inappropriate also. Some pretty words that rhyme with wolverine: green, ravine, phosphene... we might go on for 10 minutes like this. Seriously, "wolverine" has a very common ending syllable, so maybe the joke is that Jon is an idiot after all.
Jon asks his cat a question which requires both verbal response and intimate familiarity with the English language. Does he expect an answer, or is he thinking aloud? These are the mysteries of Garfield.