One tetrahedral hole is formed by one anion in the top layer and three anions in the lower layer. This tetrahedron "points up".

A second tetrahedral hole with a different orientation is formed by three anions in the top layer and one anion in the lower layer. This second tetrahedron "points down".

Click the links on the right to highlight the two different tetrahedrons. Then you can use the buttons to rotate the tetrahedrons.