I'd previously seen Chavez duetting with Lugo on film as the surprise guest at the Paraguayan election-night party.
The four Presidents seem to get a terrific high from each other and the result is that they leave the speeches behind and bring the audience into a sort of collective embrace of brotherhood.
If I were Obama, with his capacity for speaking sincerely in many different ways, I'd get the video of the Lugo-Chavez duet and learn a couple of verses of Chavez's favourite songs so that I could duet with him when we meet.
(Don't ask the tin-eared Hillary to join in though)
Photo from Roy Madron from Curitiba, BR and Montevideo, Uy