Pun.

Field Trip. To me, field trip (in this context) has two meanings. First, it is a field trip like the ones school kids take to museums and apple orchards. In the book, O'Brien and his daughter took a sort of field trip to Vietnam. The field trip was the whole trip in general. He wanted to return to show his daughter his experiences in the war and wanted to "[offer] her a small piece of her father's history" (174). The second meaning is in a more literal sense. Literally field trip; a trip to a specific place, specific field. This field trip was to the place that "had swallowed so much" (176). O'Brien wanted to return to that little field where his friend had died and where he was changed forever.