You know it’s ray tracing when…
•Reflection, transparency, other light-bouncing effects
Student image from a U of Maryland course at http://www.cs.umd.edu/~mount/427/Gallery/
Dispersion in a faceted lead crystal http://www.cg.tuwien.ac.at/research/rendering/ART/Gallery/Dispersion/
Not just multiple reflection—sophisticated modeling of materials—dispersion in a faceted lead crystal