Psychologist Simone Dalla Bella from Warsaw's University of Finance and Management and his team asked 40 volunteers to belt out, a cappella, familiar songs such as Jingle Bells and Sto Lat, the Polish version of Happy Birthday. After a number of acoustic tests, the researchers discovered that most of the singers who couldn't follow a song's pitch and timing fell into the first of two phenotypes: they were tone deaf yet blissfully unaware of it. The remainder of the poor singers had no trouble judging a proper note, yet were unable to hit it themselves, and knew it.