[OhSoHumble]

Dota players have ears that are trained for keywords. For example, the game has a minimap. Players can buy items to keep the minimap revealed and to see the movement of enemy players. The enemy team can buy an item to make it so that they aren't revealed on the minimap while they move around. This is known as "smoking" - as the item is a smoke that explodes over the team before they make their movement.

If a caster yells out "they're smoking" and the entire audience hushes in anticipation then one team knows that the other is trying to make a play and can either group up or avoid the fight.

The International is a tournament where the prevailing team wins millions and millions of dollars. Sound isolation is really important to provide an even playing field.