xkcd.WTF!?

Explanation ➲

Zoos are large encampments where various animals live in small enclosures. They're generally used as public exhibitions for amusement and education and as safe spaces for rescued and endangered animals. Many modern zoos deliberately allow different types of animals to mingle and interact, finding that it promotes enrichment and well-being. Naturally, in such cases, the zoo needs to be designed so that incompatible species (such as predators and prey) aren't allowed to interact, and good designs will allow animals space for rest and privacy when needed.

This is a fan-made version of the comic using partially transparent colored overlays to illustrate the range of movement each piece has. To show contrast, warm colors (red, brown, orange, yellow) are used for the black pieces, and cool colours (blue, teal, cyan, green) for the white pieces. Because some regions are accessible to multiple pieces, these overlays overlap and produce colors that are mixture of the originals.

Randall has created a zoo for giant chess pieces, treating them as if they were animals. He designs the enclosures to allow interactions between different species, but prevents the possibility of one piece capturing another (which is treated as analogous to one animal attacking another), as well as of escape. In the Trivia section, a coloured version of the zoo shows where different types of pieces can move. The zoo is almost completely horizontally symmetrical from top to bottom with black pieces on the top and white pieces on the bottom. The only place that isn't completely symmetrical is the entrances to the bishop enclosures.

There are many subtle "jokes" in the image that play on how chess pieces move:

• ♗ Bishops can only move diagonally. Enclosures containing them do not have diagonal walls or corners which would allow them to slip out, and orthogonal portals into their enclosures are only one square wide and at least two squares long so that they can't get through. One bishop enclosure even has a portal open to the visiting people, letting it serve as a petting zoo. Opposing bishops can safely mingle as long as they are on opposite colors, since a bishop can never move to a square of the opposite color than the one on which it currently stands. This is enforced by these mingling enclosures only having two openings, each on opposite colored squares (i.e. an enclosure only has an opening for black pieces on white squares and one for white pieces on black squares).

• ♘ Knights move in an "L" shape (two squares along one orthogonal direction, then one more square in a perpendicular direction), leaping over other pieces and presumably walls. The walls of their enclosures have been designed to prevent escape by placing blocks where they would land if they leapt over the wall, or using double-thick walls. They can also be blocked by the same portals that block bishops, although they would need to be four blocks long instead of two.

• ♖ Rooks can only move along ranks and files. They have free roam of several enclosures, though diagonal walls are able to stop them, preventing them from accessing the center mingling bishops.

• ♕ Queens and ♔ kings can move along ranks and files as well as diagonally, so their enclosures must have the same precautions as would be required for both bishops and rooks.

• ♙ Pawns can only move forward (or diagonally forward when capturing), but upon reaching the final rank (the opponent's back rank), they are "promoted," becoming a knight, bishop, rook, or queen. The pawns are in a double-walled enclosure with no doors to prevent escape after promotion.

A special feature of the enclosure, mentioned in the caption, is that there is at least one room for every type of pieces where other pieces cannot enter (except the king is always in a room with the queens). This means that even though some of the pieces can mingle with some of the other pieces they can also always retreat to a room where the other pieces cannot disturb them. For instance the top and bottom room with rooks can not be entered by any other type of pieces. In the two rooms right above and below the middle room, the bishops of the same color have their personal room. And also the two rooms to the right where black and white bishops co-exist on different colors, cannot be entered by any other type. (This is of course needed, since else there could be captures).

The pawns have their own rooms top and bottom right. The knights have a separate room from which they can jump out to the rooms with either rooks or king/queens, but no other piece can enter their personal space to the left. And the king and his queens can retreat top or bottom left where the knights cannot enter. No piece can encounter all the others (even of the same color) but all pieces can meet at least one other type of pieces, the pawns though only after promotion. But they could not meet a king. This is similar to real zoos where separate enclosures are designed to be accessible only to one species (for example, through an opening too small for one of the species to pass through), allowing animals control over their interactions.

It is unclear what would happen to the pawns after they are promoted. Whether they remain in the "pawn" enclosure or moved to their new enclosure according to their new piece type is not indicated. Also unsure is how the pawns would be repopulated if all of them were to be promoted, leaving the pawn enclosure devoid of pawns. It appears that the pawns promoting is part of the zoo's attractions as mentioned in the Banner for the black pawns' enclosure that reads "SHH! PAWNS PROMOTING." It is not explained why the visitors would need to be quiet, but if the logic of treating the pawns like zoo animals is extended then loud and rowdy humans would likely distract, disturb or otherwise prevent the pawns from promoting.

There are a couple of "interaction" areas that could have been built into the zoo design while preventing piece capture or escape but have not. There is no reason bishops and knights of the same color couldn't occupy the same enclosure, so long as there are adequate walls to prevent knights from escaping their enclosure. Additionally, it would be possible to allow visitor access to the white-bishop-on-black and black-bishop-on-white enclosure, as well as allow visitor access to the knight enclosures, however it is not apparent whether this is a priority of the zoo. Every visitor of the zoo is depicted as centered on a single square occupied only by themselves, just like a chess piece. This could perhaps imply an entire chess board "world", where humans and chess pieces coexist as separate species, both aligned to the grid.

The title text contains a pun on the word 'mating'. The phrase "mating in captivity" is typically used to refer to animals in zoos copulating, hopefully producing offspring. This is typically done for species that are endangered (in hopes of reintroducing them to the wild, and in the meantime maintaining a healthy population of their own), but in the relatively safe and nurturing environment of the zoo could become problematic if allowed to happen without a certain degree of planning. In a conservation program, much thought may be put to how to avoid inbreeding, overpopulation and social stresses amongst the animals (as well as the problems of feeding and housing all the offspring), and so males and females may be given limited and highly curated access to each other, strictly according to the identified breeding requirements.

In the context of chess, "mating" means delivering an attack from which the opponent's king cannot escape, thereby winning the game. Unlike captive breeding programs, "mating" in in this sense, would presumably eliminate a piece (or an entire side), rather than creating additional animals, and therefore is undesirable. To prevent this from occurring, kings are not kept in the same enclosure as any piece of an opposing color. In fact, only opposing bishops on opposite colors are shown as unallied co-residents of an enclosure, in this zoo, thanks to their particular method of wall-free separation.