Ignatz plays with reality.
The road disappears as if it were part of the scenery...
...but when it reappears the poof marks indicating the slamming of the backdrop show that the road is clearly below the edge of the false scene. The backdrop makes no sense in physical terms; Ignatz is playing with the fabric of the strip's fictive reality.
Herriman accents the illogic of the road by keeping the background more consistent than he does in most of his strips. This structure appears in every frame, lending the backdrop a more solid feel even as the road undermines that solidity.

George Herriman, Krazy Kat, 14 Sept. 1940; rpt. in Patrick McDonnell, Karen O'Connell, Georgia riley de Havenon, Krazy Kat: The Comic Art of George Herriman (New York: Harry N. Abrams, 1986), 101.