"The Colonel" is about a display of brute power. Forche is showing us as readers how terrifying a raw and open threat of violence is—but with a twist. Forche is also showing there is another kind of power, that of witnessing, that is perhaps as powerful as violence.
In the poem, two Americans are invited to dinner at the lovely home of a Salvadoran colonel. At first, the situation seems normal. There's a wife serving coffee, a daughter filing her nails, newspapers, a television show on. But as the guests stay longer, the scene becomes more ominous. Between a cop show in English and the dinner of rack of lamb, these lines are dropped almost casually:
Broken bottles were embedded in the walls around the house to scoop the kneecaps from a man's legs or cut his hands to lace. On the windows there were gratings like those in liquor stores.
Suddenly this becomes not a gracious dinner party but a terrifying space from which there is no escape. We find out that the colonel has a point to make, which is to intimidate his guests. Though it is not said, it seems that the context is that the two US citizens have come to talk to the colonel about ending the terror in El Salvador, when military death squads in the late 1970s were killing many people. The colonel will hear none of it. Instead, he dumps a bag of human ears on the table. He uses intimidating language meant to shut down the argument:
I am tired of fooling around he said. As for the rights of anyone, tell your people they can go fuck themselves.
The guests at the dinner party are silenced and frightened by his machismo and display of raw power. However, as the poem ends, Forche's speaker notes that the ears on the floor are listening. Of course, the literal ears are not listening, but the ears on the floor is a metaphor for the people around the world who are reading this poem and will perhaps exert pressure to end the atrocity:
Some of the ears on the floor caught this scrap of his voice. Some of the ears on the floor were pressed to the ground.
What Forche suggests is that there are moral forces pushing back against the power of violence. The colonel is not as tough as he might think.