1.   Cheng and her husband told university officials they had no idea how the stain had gotten there.

2.   Q. Leftover creosote was spilled on a concrete floor, and in summer it gets worse, smelly and the stain gets wet in humid weather.

3.   This red stain gets into the pores of the open-pored wood that mahogany is, and never comes out.

4.   If these stains get near any restoration work, they will be absorbed through micro-leakages between the restoration and the tooth surface.

5.   Tar stains also get absorbed into dental plaque and are difficult to remove.