He checks that the coast is clear, then reaches for the jar. Bart has been caught with his hand literally in the cookie jar. Bart does so, with a cookie in his hand. That jar is off-limits, Bart. Whoa, I'm scared.
Homer magically appears.
Homer leans in to make his point. Lay off those cookies. Bart swallows hard. Marge and Homer leave. Then he spots a cookie still on the counter that eluded him.