[s9w]

Well this might sound odd, but I've seen some videos.. it's very likely not just a kitchen knife. I've only seen this happening with large blades. And then it actually happens surprisingly fast. I imagine they "train" somehow to get some routine.

But either way, I can't see anyone interfering with something like that going down.

[kgwxd]

According to a source equally reliable as this (Reddit), someone tried to interfere but got stabbed.

[moooo99]

Sounds very likely. As much as one might want to help, unless your trained in self defense or you have some kind of weapon yourself, I'd imagine its really hard to interfere. Especially if the attacker is trained, the outlook for people trying to help isn't exactly great.