The joke is fine. The structure attempted is impossible because of the realities of daily-strip dimensions. Theoretically we are confused by the first panel, follow through the second, for a reveal in the third. That's the reason for splitting the single image between three panels: a gradual build and payoff, rather than making it a panel gag. Fine. But in practice, there's no way to look at this strip and ask your eye not to take in the entire, unified composition. It happens on first glance, and the eye, seeing nothing to read or focus on in the first panels, will gravitate right to Jon's word balloon.
Would've made a good "Quickie" on Garfield and Friends though.