The Gozinta Box is one of the most innovative magic tricks by Lubor Fiedler. Gozinta Boxes can be tricky to make and are relatively expensive props. The Gozinta Box Construction Kit lets you create your own props for the cost of two sheets of paper.

A gozinta box consists of two hollow cubes with perceived rib size $a$ and wall thickness $t$. We can use mathematics to prove that a gozinta box is magical. For the boxes to be able to fit into each other, the following equation needs to be satisfied: $a^3 = (a - t)^3$. This formula expresses symbolically that the volume of the outside of the cube $a^3$, is equal to the volume of the inside of the cube: $(a - t)^3$.
This equation is only valid when either the wall thickness $t = 0$, or when the rib length approaches infinity, $a \rightarrow \infty$. The absurdity of zero wall thickness or infinite cube size expresses the magical quality of the gozinta box. When the wall thickness is zero, the boxes consist of only empty space and imaginary boxes will naturally fit perfectly into each other. Cubes of infinite size are magical because they are simply beyond contemplation.