During their first Walkie Talkie session Jesse states the Sandman would not come after Sam insisting that he would be his target. This is a hint towards the aliens motive later on.
"A.C.E." is listed after cinematographer David Boyd's name in the opening credits. This stands for American Cinema Editors, of which he is not a member (he also isn't even a film editor). The correct letters to use would have been "A.S.C." for American Society of Cinematographers, of which he is a member.
When the wildlife official, Janice Rhodes, is talking to Daniel Barrett she says they will perform an autopsy on the birds. Autopsies are performed on humans, necropsies are performed on animals.
Daniel Barrett: Look, officer, this wasn't a- a cooking mess. This was like a... like a mathematician's idea of a geometry joke. Ha, I don't know whether to be pissed or impressed.