[Nisemonogatari]
5) They're being faithful to the novel.I can't really decide the rationale behind the lack of twister, but I have a few theories.
1) The director realised it added nothing to the plot, so they didn't bother showing it (but then why not cut most of that whole scene considering there wasn't really anything that furthered the main plot. Nadako's character wasn't developed, she hasn't changed at all and nothing interesting came out of her conversation unlike, say, the Arararagi's interatcion with the snail last week.)
2) They didn't have time to animate it.
3) They're saving it for the Blu-Ray release.
4) A combination of 2 and 3.