Originally I had a much much longer punchline in the final panel.  The final panel was written to read like this:

Professor/Editor: OKAY THEN.  BUT WHY THE MACABRE EMBELLISHMENTS?  ”AS WE WAITED FOR THE COUNTY SHERIFF, DAD POINTED OUT TO ME THE VARIOUS PARTS OF THE ROBBER’S EXPOSED BRAIN, SUCH AS THE OCCIPITAL LOBE AND CEREBELLUM.”

Writer/Student: I WAS HOME SCHOOLED.  MY PARENTS NEVER MISSED A TEACHABLE MOMENT.

I was okay with that, despite it being a second “home schooling” joke.  But I thought of the Twinkies thing almost reflexively as I wrote the script, then tried to fit it in as a second punchline, then realized it was funnier than my first punchline, and ditched the first punchline.