Libby’s next strip features robot Martian attacks with explosions in the background, similar to the chaotic scenes Calvin would imagine in “Calvin and Hobbes.” The joke in the final panel (“I could do better if I had more space”) was classic Watterson, who fought for a new Sunday format with fewer constraints drawing “Calvin and Hobbes.”

Friday’s strip featured a Watterson-esque panel. The lettering looks just like that in “Calvin,” while the muscular figure of Pastis is reminiscent of Calvin when he would imagine himself as a grown-up superhero. Also, the artist’s table in the panel is strikingly similar to the table Watterson drew for the “Stripped” movie poster.

“Day 5 in the series,” Pastis tweeted Friday morning. “So who is really drawing my comic strip? Me? A second grader? Someone else?”