It was called blading. They would clip a razor blade into a point. They would, put some tape at the base and hide it in their wrists if they were taped, their fingers if they were taped or hide it in their mouths. They would then slice their forehead when the time was right. Wounds were also reopened naturally if they were there. Vince McMahon did away with blading some time ago but other organizations do it and the deathmatch stuff is insane!
If you didn't see this on VICE before, Becoming A Deathmatch Wrestler, check it out. These guys are nuts!!
https://video.vice.com/en_us/video/becoming-a-deathmatch-wrestler/5d016263be407741574646c1
This is exactly right. You can see a good example of this practice in the movie "The Wrestler" with Mickey Rourke, which is partially based on the life and career of Jake "The Snake" Roberts. Mickey's character Randy "The Ram" Robinson hides a razor blade in his wrist tape before the match, then during the match, when the audience is distracted by his opponent, Randy pulls out the razor blade and quickly slices up his forehead, leaving a nice shallow cut that will give a visually impressive amount of blood pouring out, but do no lasting damage other than leaving a scar. Anything to get that big pop from the marks in the crowd. Mickey Rourke insisted on actually doing this and a lot of other things himself in the movie for authenticity, rather than leaving it to make-up or special effects tricks.
"The Wrestler" is a fantastic movie. If anyone hasn't seen it yet, I highly recommend it, not only for it's realistic depiction of wrestling, but also for Mickey Rourke's portrayal of an aging wrestler who is suffering the health problems of decades of abusing his body, with steroids and other drugs but also from the extremes of partying and performing for the fans, but who just can't move on with his life, even as he gets older and his health problems take their toll on him. Kind of like some of us aging bodybuilders, powerlifters, strongmen, and other iron sports athletes who keep on taking steroids, training way too hard, and who just don't want to admit when it's time to tone it down or quit, for our own health's sake (and I am guilty of being one of those guys.)