By killing all of the vultures in the mission, "End of the Road," the intended target will attempt to escape by running into the desert, only to be run over by an ice cream truck.
Contributed by KidDivinegon
A book found in several locations throughout the game bears the name H.C. Andersen on the cover, a real-life Danish author known for his fairy tales. His name may have been chosen to adorn the books because IO interactive is a Danish company. The copy of the book found in the chapter "One of a Kind" has a post-it note stuck to it, with a list of some of his stories that feature birds written on it:

• The Ugly Duckling" (1844)
• The Phoenix Bird" (1850)
• The Portuguese Duck" (1861)
• The Nightingale" (1844)
• The Wild Swans" (1838)
Contributed by sjrslev
After making it to the land mine testing zone in the Death Factory, it's possible to enter one of the fake houses on the left hand side of the room. Inside the room is a pig standing inside a crate eating from a bowl. Shooting the pig makes an exclamation mark appear (in a similar fashion to the Metal Gear series) which then laughs and runs across the screen, before being shot and falling over.
Contributed by DeerBoarDude
In a sniper mission, there is a very tall building in the background with two antennas that can be seen as you start. Zooming in on the building reveals a man standing on an extending ledge, looking like he is about to do a "Leap of Faith" from Assassin's Creed. Shooting the man will cause him to fall with an eagle's screech sounding once he falls.
Contributed by gamemaster1991
In the level The King of Chinatown, there are some masks on a wall near a booth where the King will occasionally eat from. Some of these masks are from the Hitman: Blood Money mission "A Dance With the Devil."
Contributed by DeerBoarDude
In the level Dexter Industries, by the Factory Compound section, you should be able to enter the main building. Inside, you are able to see a hanging nuke. Shooting at the tip of the bomb will trigger a special cutscene and an instant game over.
Contributed by Old Gollum
Kane & Lynch (from the 'Kane & Lynch' games) make a cameo in the game. You can find Kane in the level 'Welcome to Hope' near the Jukebox. Lynch is one of the people who shoots targets in the level 'Gun Shop'.
Contributed by BomberJ
The video reveal trailer ends by displaying a barcode. The numbers on the barcode teased a date (June 7th, 2011) when more about the game would be revealed. However, the company who made the trailer seem to have overlooked the barcode itself, as scanning the barcode takes viewers to an amazon listing for a bag specifically designed to store sex toys.
Contributed by DidYouKnowGaming