Saw this in a comic book in the 70s... Draw three circles on paper, cut them out. Fold in half to cut like so: in one you cut a central cross, size one radius. In another, cut a central slot, length one radius. In the third, cut two half-radius slots from opposite sides, the complement of the central cross. Now, by folding from the edge to the centre, insert the third into the second, then insert those two into the first.

Three perpendicular circles - a sphere.