Trivia: When the alien's hand comes out of the coal grate for Morgan, if you look closely you will see that the hand was already through the grate and the alien was using its colour changing abilities to hide. So if you look very closely you will that that the hand comes UP from the grate and not through it, and if you look VERY carefully you can see the outline of the hand even before Morgen says "What?"
Trivia: Ray Reddy (the man who accidentally killed Graham's wife), is the writer/director/producer of the film, M. Night Shyamalan.
Trivia: Some of the artwork done by Bo in the film was actually done by Shyamalan's daughter, Salek.
Trivia: When Graham Hess is reading the UFO book with his children in the bedroom, on the nearby table next to the lamp is a figurine of a soldier from the American War Of Independence. It is wearing the exact uniform as worn by Mel Gibson (Graham) in his film "The Patriot" (2000).
Trivia: The stories of the children's birth are actually the stories of M. Night Shaymalan's two children.
Trivia: Mark Ruffalo was originally cast as Merrill, but was replaced by Joaquin Phoenix one week before filming began.
Trivia: M. Night Shyamalan originally wrote the characters of Graham Hess and Merrill Hess in their late sixties. The two young children were not Graham's children but his grandchildren. The role of Graham was offered and turned down by both Paul Newman and Clint Eastwood. When Mel Gibson expressed interested in the script, Shyamalan rewrote the Graham and Merrill characters to be younger and the two children were Graham's instead of his grandchildren.
Trivia: M. Night Shyamalan's scene in which he talks to Hess about the death of his wife was shot a day after a member of Shyamalan's family died.
Answer: The aliens were not cloaked, not invisible. They had a chameleon-like ability to change their appearance to match their background. Recall the alien's fingers turning plaid when he held the boy. They seem to be that green color when not camouflaged. The better senses of the dogs did allow them to detect the aliens. However, one of the effects of alien presence noted in the movie was a change in personality; that is what happened to the dogs.
scwilliam