The song that Victoria and Danny play together on the piano is the aria "Habanera" from the French opera "Carmen" by Georges Bizet.
The name of the song is called "Montage" by Massive Attack. It is from the Danny the Dog/Unleashed original soundtrack.
After its cinematical release two versions of Danny the Dog/Unleashed have been published on DVD: the R-rated cut that was also shown in cinemas and an Unrated version. The latter features mostly an extended storyline and misses out some fighting scenes of the theatrical version.
