The excitement and passion at stadiums are typically found to be instigated and sustained by the presence of the percussion and brass instrument brought in by barras groups. The typical percussion instruments that are brought in and played by members of the barras at stadiums are the bombo con platillo (bass drum), Brazilian surdo drums, redoblantes (snare drums), repiques, scrappers, tambourines, cowbells, and agogo bells. The brass instruments that are typically played at stadiums by outside musicians hired by barras groups are trumpets, trombones, and euphoniums. While the collective energy and synchronization incited by the music can creates a sense of unity among attendants and supporters alike, ethnomusicological scholar Eduardo Herrera also believes that it can embolden individuals to normalize discriminatory behavior that they wouldn't otherwise do if they weren't in a crowd which would explain the some of the recorded derogatory language and violent behavior found in Argentinian stadiums.