We've entered the home of a high ranking military man in El Salvador during the late 1970s. The house is fortress during a state of siege. Outside those walls, El Salvador is being torn to shreds by a civil war.
The details of the colonel's house are described with detachment, even the broken bottles embedded in the walls surrounding the house. Within, life goes on as usual—that is, what is usual for a rich man in a poor country. The main action takes place around the dining room table, where cultures clash over the evening meal.
The apparent civility of the setting, though, is really an elaborate set-up. Once the bag of human ears gets dumped out, we realize as readers that the upscale trappings of the setting have been pulled out from under us. What we're left with is a testament of inhumanity, brought into stark focus through the contrast of the polite surroundings that the speaker reports on in the poem's beginning.