The song used in movies during just about any tango scene is about gambling:
“Por una Cabeza” is a tango song with music and lyrics written in 1935 by Carlos Gardel and Alfredo Le Pera respectively.
The name is a Spanish horse-racing phrase meaning “by a head”, which refers to a horse winning a race by the length of one head. The lyrics speak of a compulsive horse-track gambler who compares his addiction for horses with his attraction to women.
Alfredo Le Pera was a Brazilian from São Paulo, a much Italian-influenced area in Brazil. Le Pera and Gardel died in an airplane crash in Medellín, (Colombia), on June 24, 1935.