Why Is There Tension In Ernest Hemmingway's Hills Like White Elephants?

Earnest Hemmingway’s short story Hills Like White Elephants is one that is unique for its time. In 1927, when it was first published it wasn’t very well understood. The story takes place at a bar within a Spanish railway station. Unlike the norm for most stories of the time,
Hemmingway was very vague when describing his characters. The two main characters are simply referred to as “the man” and “the girl”. They a having a conversation over a few beers pertaining to the girl having a “simple operation”. They have only two choices, these choices are symbolized by the two rail tracks which travel in opposite directions. It’s also very hot, which adds more tension to the situation.
The very first sentence of the story is describing the setting.
The man notices she herself is now unhappy, and makes his best effort to cheer her up given their current situation, but it doesn’t work.
The girl then again mentions the “lovely hills” and clarifies what she meant by her earlier statement, mentioning “they don’t really look like white elephants”. As they have their third beer, the tension seems to fade for just a short period of time. The quick changes in mood through ought the story really speaks to the characteristics of both the man and girl. The reader can sense they are both at a troubled time in their life, however they are doing their best to remains levelheaded, even though at times they are frustrated. “The beers nice and cool” says the man. “It’s lovely” the girl replies.
In an instant the mood changes once again. It almost as if the man thinks to himself
“enough with the small talk,” he is no longer amused nor satisfied with simple conversation.
Tired of beating around the bush, he says as nonchalantly as the situation would allow without sounding overly anxious “It’s really an awfully simple operation, Jig. It’s not really an operation at all”. This is the first time throughout the story when the girl is referred to as anything