The sound comes from Cristiano Ronaldo's trademark goal celebration, where he jumps, turns in mid-air and lands with his arms spread, shouting Siu, a play on the Spanish word for yes. Fans began copying the shout in stadiums around the world, and clips of the celebration spread widely through football highlights and social media. It remains a shorthand for confidence and victory, because even a short version of the yell is instantly linked to Ronaldo and to scoring at the highest level.