On a grid of dots, connect 4 dots to make a square. Easy when the sides are horizontal — but tilted squares count too.
Tilted squares are real
A square with corners at (0,0), (1,2), (3,1), (2,−1) has all sides equal (√5) and all angles 90°. It's a square, just rotated.
On a 3×3 grid you can find 6 squares: 4 small, 1 medium, 1 tilted. On a 4×4 you can find 20. Counting them is a Pythagoras puzzle in disguise.