Red origami scissors, colored pens, or pencils can also prepare a red square paper. If it's not square, cut it yourself. Fold in half along the diagonal to get a big triangle. Fold the two bottom corners in half to form a high triangular folding line. Fold the two bottom angles of this big triangle in half along the height, so it is a small square.
Fold down the two bottom corners to form a diagonal of a small square. Fold the two bottom corners of the original big triangle along the diagonal. In the small triangle area where the bottom corner is located, fold the small corner in the middle outward by more than a quarter. Rotate the figure above by 180 degrees to facilitate the following folding step.
Fold the triangle above by more than three quarters (note that it is not completely folded). Fold the remaining quarter along the diagonal of the original small square. Cut the triangle below along the diagonal of the small square with scissors until it is close to a quarter of the center line.
After cutting, fold the triangle in turn, so that it becomes a small triangle. Put your thumb into the bottom of this small triangle. Fold and deform along the other two lines. Fold in half, this is the figure, like the head and body of a goldfish. Because the back is cut with scissors, it can be easily folded to make a goldfish's tail.