Due to massive amounts of debris, corpses, and a putrid environment, rats at the trenches bred at a rapid pace.
[1] The rats played a role in damaging the soldiers' health, psyche and morale and were responsible for lack of sleep, adding to the filthy conditions and unsanitary hygiene in the trenches.
In one instance, a British soldier recounted in an interview that one of his fellow countrymen had his forehead bitten while he had been asleep, with the wound being severe enough to warrant a visit to the infirmary.
[2] Trench rats contributed to many different psychological effects on the human psyche given their ability to disrupt sleep and reduce the overall quality of the soldiers' rest.
The noises rats made in no man's land during night would sometimes cause soldiers to believe enemies were mounting an attack, leading them to grow paranoid and shoot out into the empty space between trenches.
[2][8] Ammunition had to be conserved for fighting the enemy, therefore soldiers were dissuaded from using bullets to kill the numerous rats in the trenches.
[10] At other times, rat-catchers were also hired by the army to catch the rats in the trenches as soldiers could not and were scared to fall asleep due to the rodents.
Due to the high toxicity of the gases, these methods were abandoned after they were shown to have more effect on the soldiers themselves rather than the rats they were targeting.
[12] Terrier dogs were especially useful, more so than cats, as they were bred to kill vermin and for hunting purposes which was applied to eliminating rats in the trenches.
As such, trench warfare was no longer as frequently used in World War II partly because of its high cost of human life and long-lasting effects on soldiers due to post-traumatic stress disorder.
Another reason why trenches were no longer used was because in World War II, military tactics changed to favor aerial combat and with the emergence of improved technology which enhanced mobility on the battlefield, such as the use of tanks and armoured personnel carriers, which then allowed soldiers some form of protection against enemy fire while advancing against enemy lines.
In Erich Maria Remarque's All Quiet on the Western Front, they are referred to as "corpse-rats," described as having "shocking, evil, naked faces," and are said to have attacked and eaten two large cats and a dog.
[3] Prunés' portrayal instead humanizes and generates a sympathy for an animal that is often associated with the worst connotations of World War I and life in the trenches.
[16] There is irony used in the poem as an insignificant creature such as a rat could successfully complete the herculean effort of crossing to the other side, for example, when the speaker depicts of the ability of the rat to touch both a German's hand and a British soldier's hand, connecting both enemies and be "cosmopolitan" by being able to cross 'No man's land' to either the British or German trenches.
[16] In a sense, the poem portrays the rat in a positive light as the speaker believes it could perform amazing feats, such as crossing 'No man's land' with no repercussions, that no ordinary German or British soldier could on the battlefield.