The creative team behind Barney and Clyde (Gene Weingarten, Dan Weingarten & David Clark) often have fun with the conventions of the genre. The sequence published June 6, 2015 doesn't quite break the fourth wall, but it's still a clever pun (I think). (click on image to enlarge)
The idea of taking a single scene and breaking it up into panels to show motion isn't new, of course. And because it isn't, the reader doesn't immediately notice the careful arrangements of the tombstones. At least, not until the third panel. And even then, the wording is such that for many (myself included), the reference to perspective in the visual arts doesn't immediately register. It's only while reading the fourth panel that the joke hits.
And I think that's why Clyde's shown looking back to the third panel, to refer back to the location of the actual punchline. It's a subtle gag -- but a good one.