Oysters are a tricky thing. I've had oysters from slightly dive-y places that were AMAZING and then I went to Grand Central Oyster Bar with my dad and had a HORRIBLE batch that got me sick. I've eaten 25 oysters in one sitting and not been sick, so it was totally them. Knew it from the taste after two seconds but it was too late.
I've become a slight oyster aficionado from a local joint that has an awesome selection, so I like trying different kinds. I chew mine a little. I once got a cherrystone clam (never again), that was half the size of my face and somehow got it into my head I could eat it in one bite. Nearly choked and my friends STILL laugh at the faces I was making. So silly :p