Your brain is actually really good at hunting flies, but in a very specific way. To find a fly just stand in the corner of the room and stare at a random object in the room. Your peripheral vision will find the fly in no time because we are very away of those changes as part of our reflexes.
Another fun fact is your tongue is extremely tactile. Look at any object and your tongue knows EXACTLY what it would feel and taste like to lick it. Try it out yourself!
So, I'm the guy who actually helps flies get out of my apartment and I don't know, if this info made its rounds in the fly hood, but last two times I had a fly in here, I hadn't even fully opened the balcony door yet and fly bro was outta there.
Made me feel like a gentleman, holding doors open and shit.