One example that goes in the opposite direction is the difficulties researchers have had in coming up with an animal model for studying the risks of tobacco exp

One example that goes in the opposite direction is the difficulties researchers have had in coming up with an animal model for studying the risks of tobacco exposure: http://www.ncbi.nlm.nih.gov/pubmed/17661225 http://www.ncbi.nlm.nih.gov/pubmed/17661225