What do the soldiers consider odd about the International Trench in the novel, Under Fire?

An odd feature of "No Man's Land" running behind the actual fronts, the International Trench has French and German sections that are not marked in any way. It meanders and is partially collapsed. A group of Bertrand's Squad, in search of matches, stumbles into the International Trench, hides from a lone German sentry, kills him, steals his possessions (including matches), and races back. Stopped at the entry to the French trench system, they learn where they have been. During the slaughter on Hill 119, French survivors flee into the largely-collapsed International Trench, which is filled with dead Germans.