If you think Bay would even bother to explain that, you are giving him too much credit.
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Some on set pics:
http://imgur.com/a/9qsiA
Karate originally meant "China Hand" (唐手), or literally "Tang" Hand (in reference to China's Tang Dynasty). It was later changed to mean "empty" hand (空手), but empty just means without specifically crafted weapons like swords, spears, bow and arrow etc. The weapons that are used by Karate and Ninjutsu are arms used by peasantry because they're just regular tools.
e.g.
nunchaku - a type of flail used in farming
sai - a compact pitchfork
bo - staff used to transport loads (e.g. buckets, baskets etc.)
tonfa - handle for a mill
kusari-gama - sickle attached to chain
etc.
Katana were only used by ninjas though, not karate. Karate was basically a martial art practised by Okinawans for civil defence, whereas Ninjutsu was practised by Japanese peasantry who took arms in guerrilla warfare against Samurai, so they would used crafted weapons like Katana, shuriken (ninja stars), tetsuboshi (caltrops), bow and arrows etc. They would also used smoke bombs and improvised explosive devices. Basically the Ninja were the feudal Japanese equivalent of the Viet Cong or Taliban in modern times. The word "Ninjutsu" (忍術) itself literally means "The art of stealth." The ninja often saw themselves as kinds of freedom fighters etc., whereas the Samurai saw them as cowards. In a few rare instances there were alliances made between Samurai and Ninja clans, e.g. Hattori Hanzo (hence the reference in Kill Bill ;))
Is that Will Arnett in the photos?
So much for having suits with CG faces ala Where the Wild Things Are.
^What am I watching?