She asked for an example American folk song (she is Israeli). Without thinking I said “Tom Dooley”. We sang it and sure enough, entirely from the pentatonic scale (the only exception is the high part sung with the chorus, which includes a 4, but this was probably added later by the Weavers, sounds like classic Pete Seeger counterpoint). Another notable feature about Tom Dooley is that the chorus has the same melody as the verse, which adds to the monotonous quality. So maybe, rather than looking for other songs with two chords about murder, they should have been looking for other pentatonic tunes. One that struck me today is “Paradise”, a John Prine tune I love that also has the verse and chorus sharing the same melody, and sure enough, all pentatonic all the time. Also two chords, maybe also about a murder of sorts (“Mr. Peabody’s coal train has hauled it away”).