With a simple test, Dean Jones, professor of medicine at Emory University, says he can peg a pet owner. “We can pretty much guess who has pets based upon what’s in their blood,” he says. That’s because an egg-killing chemical used in tick and flea collars also makes its way into owners’ systems. That’s as far as the information goes at this point, though. Are these chemicals dangerous? Are they bad for your children’s health? No one knows. At least not yet.