No Budget: Was made on $500,000. Gareth Edwards made all the CGI on his home computer, most of the locations were stolen, and many supporting characters were simply bystanders recruited to improvise scenes on the spot. The boats and trucks in trees were probably left there by previous hurricanes.
Reality Subtext: The U.S border has walls at high traffic areas, and the rest is patrolled, all to control the flow of aliens in the immigration sense.
Romance on the Set: The actors playing Andrew and Sam were boyfriend and girlfriend in Real Life, and married in June 2010. Word of God says that their preexisting chemistry is what got them the parts in the first place.