http://www.wired.com/underwire/2010/09/monsters/
"Edwards also used Galveston, Texas, as a location for a key sequence after Hurricane Ike ripped through the Gulf Coast port city.
“If you Google ‘post-apocalyptic,’ a lot of things comes up that are post-hurricane areas,” he says. “We seized our opportunities and found flooded homes and freeways that scoop out of the earth because of a flood. The movie is full of these little random moments that if you’d try to create them from scratch, it would cost thousands of pounds.”
A champion of improvised dialogue, the director cast nonprofessional actors he met along the way. Initially wary, civilians warmed up to Edwards each time his Spanish-speaking producer dropped the word “extraterrestrial.”
“When we’d first arrive in a town with our cameras, everyone looked at us nervously: ‘What the hell are you doing here?’” Edwards recalls. “Our fixer would explain what we were doing and as soon as they heard ‘extraterrestrial,’ they relaxed and said, ‘OK!’ It’s like the whole of Mexico wanted to be in a monster movie.”