Here, various jokes are represented as a grid of animal footprint diagrams. In comic-book-reading order, with which you should have no trouble following, here are the explanations:
- Cat Just a cat’s footprints - this non-joke is used as a foundation for the jokes that follow to build upon. If it helps, you may think of it as a “control group.”
- Moose and squirrel A reference to children’s show The Rocky and Bullwinkle Show.
- Longcat a reference to an internet meme of the “lolcat” variety.
- Mouse riding Bicycle from The Mouse and the Motorcycle children’s series.
- Rabbit stopping to use hair dryer It’s funny because rabbits don’t use hair dryers. It is also a setup for a homographic pun.
- Legolas An “elf” from the Lord of the Rings movie series who leaves no footprints (get it?).
- Bobcat on pogo stick Something random and wacky.
- Knight The footprints move in the manner required of the knight piece in chess.
- Kid with Transmogrifier A reference to the children’s comic Calvin and Hobbes.
- Kid with Duplicator A reference to the children’s comic Calvin and Hobbes.
- Prius A topical joke referencing the malfunction of the new Prius’ braking system.
- Higgs Boson The tracks in this diagram resemble the output from the Large Hadron Collider that may prove the existence of the Higgs Boson particle.
In summary children’s series, lolcat, children’s series, homographic pun, Lord of the Rings, random/wacky, chess, children’s series, children’s series, topical joke and physics.
Note: you may consider the previous summary to be of this comic strip, or of the entirety of XKCD, the choice is yours.