I have a crocheted Appa in our teddy bear basket downstairs and I'm waiting for the day when Lucy realizes that one of those critters is mythological. We have a regular bison teddy (teddy bison? bison bear?) from our trip out to Nebraska and yeah the sky bison does not look at all like a regular bison, with the extra legs and the coloring and the massive tail.
Explanation: Appa is a sky bison from a kid's show. In the real world, you can buy bison meat in several forms including ground (like ground beef). The comic plays on the sky vs ground dichotomy.
Text:
M: That is Appa, a sky bison.
L: You can't find those in a grocery store.
M: Nope, they only have ground bison.
L2: *obliviously playing with Appa*