Fairies

When reading the play I had the feeling that the fairies weren't perceived by the humans in the play. Oberon says he is invisible and what not. The 1981 version of the movie used this interpretation as well, although in quite a creepy manner. After watching the movie, when I read Titania and Oberon accusing each other of affairs with Theseus and Hippolyta, I don't see it as a physical affair, but as more of a playful thing, for example Titania enchanting  Theseus and making him act silly and high and dancing around in the woods and just sitting talking to himself, or her, not knowing in fact what he was doing. Also did anyone notice in the movie when all the little fairy children gathered around bottom (funny he is named bottom an he turns into an ass) that there is one girl in the background just bobbing back and forth for no apparent reason? The film was obviously made on a very low budget, but I am unsure as to why the girl was bobbing. It was quite hilarious, but does anyone have any ideas?