Furies make their first appearance in San Francisco. They are present in almost every body of water; they will normally simply circle around. When Nathan Hale enters the water, the Furies present in the area will automatically focus on him and chase him down. Furies possess an instant death attack - should they swim to the player close enough, a special scene will play in which the Fury will grab Hale and then fatally bite him. They can swim at a faster pace than normal to attack the player, and will pursue him until either they catch him or the player leaves the water.
In general they are used to render bodies of water as instant death traps, though sometimes players are forced into situations to quickly swim through Fury-infested water. Due to gameplay mechanics Furies are immune to all weapons and cannot be killed, so engaging them is just a waste of ammunition. When seeing water, it is advisable to search the area for Furies before attempting to enter and swim through it.
Joseph Capelli discovered frozen Furies trapped under a frozen lake in Central Park. Presumably, the Furies in New York City were accidentally frozen by the wormhole's weather-changing effects.
The Fury's name is derived from the Furies, or Erinyes from Greek mythology in which they are female deities of vengeance or supernatural personifications of the anger of the dead.
Furies strongly resemble the Sharkigators from Insomniac's Ratchet & Clank which they also instantly kill the player if they stay too long in the water.
Despite the fact that Furies are invincible, they still bleed after being shot.
No matter where the player is facing, the game will still show the Fury grabbing Hale as if he was facing towards it, should Fury come close to him.
A Fury resting on the car.
In Chicago, a Fury is briefly seen climbing onto a car before re-entering the water, resembling a seal. It is unclear to what extent these creatures can move around on land, though since they never attack the player while they are climbing on other cars, it is doubtful they are particularly effective there.
Furies are invincible as a gameplay mechanic to deny the player access through flooded areas.
Furies were originally going to be able to crawl on the ground and attack you. Concept art shows them armed with what looks like Reaper Carbines.
