They just bend their arms into pretzels and hold them squiming on the ground.
"Gentle art" my ass...anyone who thinks it's gentle hasn't done any.

Martial arts don't make people gentle either; they just provide techniques.
It looks like a somewhat okay knife though.
I've done aikido for years (yoseikan style)...I think perhaps the Aikikai wasn't as let's-all-sing-kumbaya perhaps when he started as it is today.
Aikido though, particularly in the aikikai, is really, really strongly reinforced with Ueshiba's teachings, almost to a quasi-deified level, and indeed, the students of almost all aikido schools, barring the Tomiki clan, are never even allowed to compete. These days, most aikikai schools don't even spar.
Serious aikidoka are one of the most monk-like groups of JMA out there, maybe along with the iado guys. Even these days, many years later, I don't compete. And the Yoseikan is a much more old-school, aikijujutsu sort of place, much more fighting oriented than the aikikai.
It's true that being a serious aikidoka doesn't make you impervious to being a mean person, in the same way being a priest wouldn't, but we still find it remarkable when priests or pastors have a serious failing, and I think JMA would and do find it remarkable that a hardcore aikidoka would do this thing too...
I've done many styles over the years, and virtually all make a big deal out of pacificism, but really none have driven it home like the aikidokas--in the aikikai, you're usually not even allowed to punch someone in pure self-defense. Virtually the entirety of damage someone sustains must be from their own energy--from a technique perspective, it's almost sort of a non-violent violent resistance...
Anyway, I just find it interesting, and disgraceful.
But the knife is still cool, lol. Alright, I've derailed the conversation enough.