The July CatWatch edition has a warning about the toxicity of pennies produced after 1982.  I never thought about the odds of a cat swallowing a penny or even a nut or bolt made of zinc.  A lot of them are zinc (nuts/bolts).  Check your cat carriers and dog/cat crates for any loose nuts/bolts.  Good reminder to keep coins out of the reach of cats or dogs.   Apparently, the acids in the stomach eat away the copper coating thereby exposing the zinc.  Fortunately, the cat in the story survived. 

They don't have the article posted yet, but here is another reference from Cornell.

http://www.ansci.cornell.edu/plants/toxcat/toxcat.html

I looked at an Ex-Ray of a cat who had a penny in his belly. they did have to take it out. There it was, just sitting in the kitties belly.