Explanation 1: Jon was in a hallucination in the first two panels, and has just come out of it in the third.
Explanation 2: Jon has gone mute.
In both scenarios, Garfield is eating Jon's cereal and taunting him with it.
What happens when you remove Garfield's thought bubbles, and in some cases explain the comic strip like Joe Mathlete Explains Today's Marmaduke?
Explanation 1: Jon was in a hallucination in the first two panels, and has just come out of it in the third.
Explanation 2: Jon has gone mute.
In both scenarios, Garfield is eating Jon's cereal and taunting him with it.