(at around 20 mins) Arthur opens the curtains and the light reveals three statuette monkeys. These are the Japanese "three wise monkeys," Mizaru, Kikazaru, and Iwazaru, who "see no evil, hear no evil, and speak no evil." Although their origins (and the phrase accompanying them) are disputed, it is generally believed that they are part of a Japanese (particularly Buddhist) "Golden Rule" to avoid spreading evil.
The location used for the fictional Nine Lives Causeway (leading to Eel Marsh Island) is Osea Island's tidal causeway situated at the estuary of Blackwater River in Essex, England, United Kingdom. Due to tidal conditions, the cast and crew were restricted to only 4 hours of working time per day at that location.
When Arthur Kipps (Daniel Radcliffe) first visits the cemetery on Eel Marsh Island, a fleeting scene shows "The Muddy Boy" (the ghost of Jennet's drowned son) standing inconspicuously beside one of the tree trunks in the background.
The "happy" ending in which Arthur and his son are reunited with their wife/mother in the afterlife was a last minute addition after test audiences felt that the film ending with them both being killed by a train was too depressing.