Ok, I apologize for taking so long, but I wanted to be sure I gave you the correct info.
The black marks in the can is caused by tinning, it's a reaction from the tomato sauce and the can and is harmless. The metallic taste is from it being in the metal can so long. The American Canning Society says that they have opened cans that are 100 years old with food still being edible.
I would not worry about it unless you start throwing up, if you start feeling sick, vomiting or develop bad diarhea, I personally would consider going to the hospital with the can in tow.
I hope this helped, and I hoep you don't get sick. Is this a can you recently bought? How did you wind up with such an old can of food?
Lisa
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