I wrote "I watch the white fly." That was an error, can someone explain to me please?
"To watch" should more properly translate "guardare" in my opinion; not sure if it should really count as an error though. As for "la mosca bianca" I'm not sure if the double entendre is premeditated (though it's likely) but in Italian it's a metaphor for something/someone rare and exceptional, outstanding, unique among its peers.
You can see something accidentally. To watch it is more deliberate: to pay attention to it, to stop to study it. You might see a fly, then stop to watch it.