A kids' card game: any two cards you draw share exactly one picture — never zero, never two — and the first to spot it wins. It feels like luck. Peel it: those cards are the LINES of a finite projective plane, and 'two cards share one symbol' is the oldest law in geometry — two lines meet in exactly one point.
Seven cards, seven symbols, three per card — the Fano plane, the smallest projective plane (order 2). Its defining axiom: any two lines meet in exactly one point → any two cards share exactly one symbol. The page verifies this across all C(7,2)=21 pairs live: 21/21 share exactly one, 0 share zero, 0 share two. Tap the matching symbol; 'show the plane' draws the two cards as two lines crossing at their shared point.
The cute symbols (🍌🎈⭐…), the 'spot it fastest' race and the toy framing are the costume; the real Spot-It deck (order 7, 57 cards) is scaled down here to the Fano plane so you can see the whole thing.
A card game instances one small plane — it does not prove that projective planes exist for every order (they don't: order 6 and 10 are impossible); the toy shows the axiom, not the deep classification.