A cute fox from one square — and the triangles and symmetry inside it
Fold a square corner to corner. The diagonal cuts it into two identical triangles, each with one 90° corner and two 45° corners. Two of its sides are equal, so it is an isosceles triangle. The long edge is the diagonal of the square, about 1.4 times as long as a side.
Fold the triangle in half and open it again. This crease runs from the square corner to the middle of the long edge. It is the fox's line of symmetry: it splits the 90° corner into two 45° angles, and the left and right halves of the face will be mirror images of each other.
Fold each side corner up and over, so the folded edge points to the middle of the slanted side. The edge has turned by 45°, so the crease cuts that turn exactly in half: it is an angle bisector. Do it on both sides and you get two matching ears. Finally, fold the top point down and behind along a line one third of the way up. That crease is parallel to the long edge, and the point sticks out below as the nose. The nose is still a 90° point, because it is made from the same two 45° sides.
Notice that the finished face is exactly as wide as the side of the square you started with. Pause on any step and ask the tutor why the ears match, where the angle bisector is, or why one third makes such a good nose.