Impalements v. Protruding Object

What is the dividing line between an impalement and a protruding object? Frankly, I'm not sure. But apparently in 100 horror films released since 1975, impalement has been the most common "pain inducer," followed by protruding object.

The article's list is odd, because it appears to contain 91 films, some of which go back to 1960. At any rate, I've seen around 46 of them (the uncertainty is due to my inability to remember which Friday the 13th and Nightmare on Elm Street movies I've seen. They kind of blend together).