One may recall that a side effect of female variant #5 is pheromones that potentially make them attractive to people who normally wouldn't find them attractive, and Nanase is assuming that that's why she's feeling an attraction to Ellen.
I'm not sure if sneezing while someone is talking about them is cultural thing specific to Japan, but I do know I've seen it in a lot of animes. Given that all anime is a 100% accurate representation of Japan, I'm going to assume it is.
I remember being a fan of Shanghai Noon and Knights, though I haven't seen either movie in years. I enjoyed Rush Hour when I first saw it in theaters, but I think what I actually enjoyed was hanging out with people at the movies. It didn't hold up well for me when I watched it later.
Commentary added for December 31, 2014