I was playing a set on the roof of Leg City Skyscraper, and half way through I noticed, at the side of the screen, a pigeon. Except since I was concentrating on the centre of the screen, I didn't. I saw a bright blue, glowing, round thing, and my immediate thought was to go and collect the hidden orb. Which led me to mess up huge sections of the song, and only get three stars.
Damn you Crackdown.