Q: Is it true that chocolate is really bad for dogs? My dog got into some chocolate cookies several years ago but didn't seem to suffer any ill effects. Is this chocolate thing a myth?

-- G.D., Miami, Fla.

A: Chocolate is indeed toxic to both dogs and cats. Chocolate is made from cocoa, and cocoa beans contain caffeine and a related chemical compound called theobromine, which is the real danger. The problem is, dogs metabolize theobromine much more slowly than people do. It builds up in their systems and can cause hyperactivity, tremors, high blood pressure, a rapid heart rate, seizures, respiratory failure, even cardiac arrest.

Cats and dogs have potentially the same response, but cats apparently aren't as interested in eating the stuff as dogs are.

I can't say for sure why your dog didn't become ill. I'm not endorsing chocolate for any dog, but one small chocolate chip cookie is not as likely to cause problems for a large dog as it might for a smaller pooch. Also, baking chocolate and dark chocolate contains more theobromine than sweeter chocolates.

In any case, be careful about leaving chocolates or chocolate-laced goodies out for Santa. (He doesn't need the calories anyway.)