When Captain Torres enters the barber shop, he says, "It's hot as hell." This is an example of overstatement. He says more than what is true in order to emphasize the truth: that it is incredibly and unbearably hot.
When the barber describes the sound the razor makes as it "rasped along" the captain's thick beard, he employs onomatopoeia. This is a word that actually reproduces or mimics the sound it describes. The word "rasp" is an example of this literary device, as we can certainly imagine the scratching, rasping sound of the razor blade over a four-day beard.
As the barber shaves the captain's neck, he considers how easily "One of the tiny pores could be opened up and issue its pearl of blood." This is a metaphor, a comparison of two unalike things where one is said to be the other, because a drop of blood is not literally a pearl. However, one drop could be similar in its round shape, and blood is certainly something of great value, like a beautiful pearl would be.
When the barber describes the waves of violence in the town, he thinks that "it goes on like this until everything is a sea of blood." This is another metaphor, comparing the amount of bloodshed to the water in an ocean, emphasizing just how prevalent the violence is.
Using another water comparison, a simile this time, the barber imagines what it would look like if he did cut Torres's throat, how the blood would "inch" along the floor "like a little scarlet stream." A simile compares two unalike things using the word "like" or "as."
Ultimately, the story ends with a significant irony. All along, the barber has believed that "Torres did not know that [the barber] was his enemy. ... It was a secret shared by very few, precisely so that [the barber] could inform the revolutionaries of what Torres was doing in the town." Torres's relaxed behavior in the barber's chair would seem to confirm this. However, as Torres leaves the shop, he says, "They told me that you'd kill me. I came to find out." Thus, situational irony is created, as what we expected is not actually what happens. All along, the reader feels the tension created by what seems like dramatic irony, as we think we know more than Torres and that he is unaware of the threat the barber poses to him. However, we now realized that he did know, and this irony is shocking.