The key to understanding how this quotation reflects the collective trauma of war lies in analyzing the thoughts of the veterinarian. As a vet, his peace-time occupation is healing, helping animals and their owners by repairing injuries. In this passage, however, he is not acting as a vet but as a soldier, and not just a passive soldier but an actively attacking fighter in battle.
The soldier is using his bayonet to stab his victim and is feeling the sensation of the knife entering the victim's body. He has probably used a knife to cut into a body before, as a veterinarian operating on an animal he is treating. He understands what it means to cut into a body - internal organs are "split in two" as the knife cuts into the flesh.
But never before has the veterinarian violently cut into human flesh. The experience is traumatic because he fully understands and identifies with what he is doing to the enemy's body. As a soldier, he is following orders and doing what is required. As a veterinarian, he is violating his training and instincts, and his mental reflections indicate the inner conflict that is resulting.