It has been suggested, even by the director himself, that Green's films take a lot of influence from the works of fellow Texan Terrence Malick.[13] Malick himself served as an executive producer of Green's 2004 film Undertow. Green has suggested that no other director had used voice-over narration so well, citing Malick's classic 1978 film Days of Heaven as the principal source of inspiration for Undertow.