Probably the fly crawling up the wall was fake. Looks like it's magnetized.
Not probably, but for sure, the crawling fly was a fake; Cusser is right. Its confirmed by Tonino Colli, the director of photography, in his interview on the OUATITW bonus DVD. What is interesting for me is that magnetized fly had not crossed my mind how to resolve it despite I am magnetized by this masterpiece film. By the way, Tonino Colli mentioned, that they tried a fake fly for the shot in which there is the real fly now, but it did not work.
Anyway, there is another fly I have noticed. During the scene in the saloon, when Frank strives to pay back Harmonica 5k bucks, in one moment a fly appears on Frank's elbow; there are 3 versions of mine why the fly entered the history:
1. nobody noticed it
2. they noticed it, but the concrete shot was so highly appreciated that they sacrificed the fly
3. they noticed it, but did not pay attention considering it as a natural occurence
Be it as it may, I think that that unfamous fly was just a natural part of the environment where the shooting took place
