The GI tells Claire that K rations are called "s**t on a shingle". This is total nonsense. The term refers to creamed beef on toast. This is made from canned meat that has been chopped and fried, with flour added to create a gravy. This is then ladled onto a slice of toast.
The GIs were separated from their unit on D-Day and found their way to a British field hospital, which means that they had just endured days of combat, sleeping in fields and such. Despite this, their uniforms, helmets and equipment are in clean, pristine condition.
Claire uses the term "trenchfoot" when speaking with another character, but the character doesn't blink an eye or ask what that means. The term is from World War I , in which massively long and complex connecting trenches were dug and inhabited by opposing armies literally for years. Trenchfoot is a description of the rot that happens when men spend weeks standing in wet, muddy trenches.
Claire warns Angus about 'trenchfoot', yet he doesn't ask what that is. The term was coined during World War I when soldiers would spend months in muddy, water-filled trenches, causing their feet to be overwhelmed with bacteria and begin to rot.
At 26:22 the start of a contrail from a jet plane can be seen in the sky at the top right.