That looked like some great special effects. Although it says in the trivia it was just muslin stockings spun around. It's amazing the effect that had from something so simple.
shareCreepiest, most nightmarish tornado ever in any movie, including recent computer-aided tornado movies.
shareThat was amazingly realistic for the special-effects technology they had in the 30s. The only flaw was that it was in the exact same position in almost every shot, save for the first one.
shareI don't think any praise for that effect needs to be qualified at all.
Regardless of when it was done and with what technology it was made, that tornado is still freaking awesome by any metric. In fact, to my eyes, that tornado is more realistic than any CGI tornado I've yet seen because they actually *filmed* a real vortex. That it was made out of spinning fabric instead of wind and detritus doesn't matter. It looked like a real tornado.