Cats are twice as likely to get cancer if their owner smokes. The toxins from cigarettes are inhaled and get on their fur—which is licked up when cats groom themselves.
Bertone, Elizabeth, Laura Snyder, and Antony Moore. “Environmental Tobacco Smoke and Risk of Malignant Lymphoma in Pet Cats.” American Journal of Epidemiology. 156(3). 2002. Web.