Panel 1: Space-Guy Mike and Bat-Lawrence yell TRICK OR TREAT as Canadian Mrs Wilson puts popcorn balls into their treat bags while John smiles somewhat crypticly.
Panel 2: As he reaches into their bags about five seconds later, he says "Just a minute...MUNCH-CHEW-CHOMP...I'd better make sure...CHOMP-CHEW-GLUT...that this stuff is safe..."
Panel 3: "...you can never...MUNCH-SLURP...trust anything homemade." Lawrence says that it's a good thing that John was the point-man for trick-or-treating.
Panel 4: Since he's, like five or six or something, he isn't being ironic when he praises John for protecting them from four popcorn balls, two taffy apples and six pieces of homemade fudge.
Summary: As was said yesterthread, the razor-blade in the apple myth is a moral panic and John is a greedy pig who wants to spin it to fill his face and leave Mike to eat crap. At least we find out Monday that Mike's selfishness, pettiness and greed keep Lizzie from rotting her teeth and potentially choking on hard candy.