They shout it three times.
“Que o la tomba serás de los libres,
O el asilo contra la opresíon!”
(Either you be the tomb of the free, or the refuge against oppression!)
Whenever I heard Chileans sing their national anthem, I noticed how they always shouted these lines. People went from singing, to raising their voices in unison. A local teacher told me that during the Pinochet dictatorship, this part of the national anthem became a way for the people to empower themselves. The habit has carried on.
Here’s a version of the modern, official anthem- (with English and Spanish lyrics)