i was in a local gun shop today and a guy walked in with a big bandage over his right eye. he had this little 9mm in his hand that the dealer later described with disgust as a suicidal cheapo. now this gun had a hole purposely machined in the back of the slide and it turned out that while he was shooting it the firing pin exited through that hole and gave him the need for the eye patch. then he asks about gettin it fixed. the dealer looked him in his one good eye for a sec then says real matter of fact "why would you want to?".

Maybe the hole was there so that in case of a failure, you could manually strike the back of the firing pin.