Starting after the chorus at 4:02, Guantanamera, the singer goes into a mode that I don’t recognize. Not minor, not major, or any of the other modes that I know of. Is there a term for what he’s doing here?
I don’t know the answer to your musical question, but Holy Moley! what a fabulous, goosebump-inducing video presentation of that song! Love the masterful editing and the different scenery and the montage of performers-- I welcome this gorgeous earworm.
Oh yeah it’s a longtime favorite of mine. I just could never quite figure out what that one guy is doing.
I can’t hear anything especially unusual there?
The song is fairly solidly in G major. There’s a quick circle-of-fifths turnround at about 3:57, could that be what you’re hearing?
I don’t think it’s a mode as such, he’s just choosing to sing some notes not within the key – in jazz, this would be “playing outside.” For example he’s using the minor 3rd scale note within a plain-old major mode (Ionian), which contains the major 3rd but no minor third.
So if it’s not a mode, there must be a name for what he’s doing? I don’t think this guy randomly decided to throw in a minor 3rd, I feel like I’ve heard this in other Latin songs. Not just the notes, but the whole wailing style that he’s doing.
You bet! I listen to a lot of latin music, and I have heard a flock of that sort of excursion. Sometimes it’s so sbtle, and so quickly in-and-out, that you only realize that something has happened after it passes. If that tickled you, watch Playing for Change’s La Bamba.
Dan
False relation?
He’s just throwing in a minor 7th in a song that doesn’t have any minor 7ths, but he’s leading into it with a major 7th.
Seems really unnatural to me, like singing a tritone interval. Couldn’t do it with a gun to my head. But it’s quite an effect if you can get it right.
The word you’re looking for is blue note.
I think that’s right. This would explain why I couldn’t even peck it out on a keyboard.
It should not be surprising that blue notes are not represented accurately in the 12-tone equal temperament system, which is made up of a cycle of very slightly flattened perfect fifths
My ear just isn’t shaped like that.
You may find this music history video interesting 
P.S. as Johanna’s link points out, one possible use of a “blue note” is to create a seventh or eleventh, etc. harmonic, therefore making the music less dissonant. That has to be distinguished from throwing in “outside” notes for a deliberate dissonant effect.
