One health problem they hide is heart disease, meaning it can progress to become life-threatening before it's noticed.

About 10 to 15 percent of cats have some type of heart disease, according to John Rush, a veterinary cardiologist at Cummings School of Veterinary Medicine. 

"Often, cats with heart disease show no signs that something is wrong with their heart, and thus the signs that they're getting in trouble come on very, very suddenly," Rush said. "They're fine one moment, and they're in a lot of pain or have marked difficulty breathing the next moment."