In the secret area in the corn field, there is a darkroom with several undeveloped pictures. If you wait long enough, one of them will develop into a photo of an area you’ll see later in the game. Another photo in the darkroom shows the creature from the ending.
Much later in the game, during the ending sequence as you’re leaving, you’ll pass a large image that shows the hill you will reach when you exit the facility.
You can find many large letters that resemble the letters used in the city area of the developer’s previous game, Limbo.
At the start of the game, if you look very closely at the plants around the trees, you can make out the silhouette of the main character of Limbo.
In the CEO’s office, there is also a cup depicting the main character of Limbo.
There are a few clocks in the game, and they will all display the current real-world time (based on the time you’ve set your console to).
When you use a chest of drawers to block the door so the dogs can’t follow you, jump on it to make the drawers slide out. One of them will reveal a Game Boy.