The question is about a literary depiction of a 'nicest moment' for POWs under German custody during World War II, but lacks specific textual references to provide an accurate answer.
The question refers to a scene from a literary depiction of World War II events related to prisoners of war (POWs) and does not specify a particular moment described by the author as one of the nicest moments. Therefore, I cannot provide an accurate response to the question as asked without more context or information from the specific text the question is referencing. The experiences of POWs under German custody typically involved forced labor, inhumane treatment, and exposure to the horrific aftermath of battles and atrocities - themes commonly explored in literature and historical accounts. It is important to consult the specific work in question to determine the author's portrayal of such a 'nicest moment' amidst the harsh realities faced by the prisoners.
Although this may seem strange, it is important to understand that the context of war and survival can lead to unique perspectives.
This moment is likely described as one of the nicest by the author because it provided a break from the other horrors of war and allowed Billy and the other POWs to remember what it felt like to be 'useful' or 'productive.'