Avoid using sand, corncob bedding, cedar, or pine products. Sand can become an irritant to a snake’s belly scales and can cause intestinal impaction if ingested, and the resins in cedar and poor-quality pine shavings can cause respiratory distress in your python.
http://quamut.com/quamut/ball_python...ll_python.html

This came off of a website about substrates. pine and cedar Chemicals can result in RI