Easy. First it makes a loud snapping sound and then it folds in two. I remember watching that game. I was nauseated at the sight.
There are some classics in there.
Earl on Robertson, Earl and Tatum at the goal line.
Steve Atwater's hit on Okoye. Atwater was wired for sound that game - if you ever get a chance to hear the live version it's classic. Okoye's career seemed to take a nose dive after that day.
Tatum's hit on Sammy White in the SB
Don Beebe getting bounced on his head and not getting hurt.
Even Ernest Givens gets in on the action.
Just seeing Ronnie Lott and Jack Lambert brings back memories.
There's some oldies but goodies in there. Butkus, Karras, etc. The Karl Kassulke hit on Greg Landry was on highlight films for years back in the early 70's.
Yes, it was a game played by a different set of rules back then. If they allowed the clotheslines and yanking down by the helmet today, we wouldn't have any players left by midseason.
You also see a lot of "leading with the helmet" in some of the footage. That's one of the modern rules that's a bit subjective and tough to call in real time and it often ends up resulting in some ticky-tack calls.