What can I do ? It was on may 25,2012 , it was on hot spicy sandwich from McDonald's

Did you immediately show it to them?

A coworker had gotten part of a grasshopper in his Arby's super roast beef sandwich (noticed when he took a bite in the parking lot), so after he threw up, he showed it to them and got lots of coupons. (He never ate there again.)

If you did not immediately report it then there is nothing you can do. Likely, if you do report it you will get some coupons for a free meal if anything.

Ask for another sandwich, free. :)

Unless you showed it to them at the store exactly when it happened, there is little you can do now.

There is often some "foreign" matter in some foods, I given an example of the bakery I worked at for a short time as a young man, the yeast in large vats ( about the size of a small room) rise over night, in the morning there may be rat or mouse droppings on them, they just turn the machine on and it is mixed in. ** this was a major bread company, said that a certain percent of other material was allowed in mix.

But if you had showed it to them at the store, got a report made of it, now you can try of course but hard to prove it really happened.