It's not at all uncommon for game developers to pay homage to the work of their peers or even their own past work by including hard to find Easter eggs in their games. What is, perhaps, a little surprising, however, is just how long some of these secrets can go undiscovered despite millions of people buying and playing the games in which they are hidden. Some of them are so hard to find, in fact, that the developers who hid them sometimes need to give players a little nudge. Enter Jonathan Cooper.

Cooper is an author and animator who has worked on some of the biggest and best selling series in gaming. These include Mass EffectAssassin's Creed and The Last of Us, although he recently found himself talking about another Naughty Dog IP following an Easter-themed tweet from an independent game designer. Jan Willem Nijman asked his fellow creators to share the best Easter eggs they've ever hidden in their games, and Cooper was more than happy to oblige by providing details about an Assassin's Creed secret hidden away in Uncharted 4.

RELATED: New The Last of Us Easter Egg Found in Uncharted 4

Cooper actually hid Assassin's Creed style synchronizations in both of the Uncharted games that he worked on. While the Assassin's Creed Easter egg in Lost Legacy was discovered long ago, the one hidden away in Uncharted 4 remained a mystery to most players until now. As for why so few people had stumbled upon it, the animator speculated that it may have been due to players needing to not touch their controllers for a few seconds; something that most would be unlikely to try even after climbing to the top of the clock tower. While perhaps the most interesting, this was just one of many revelations to come out of the Twitter exchange.

Several indie developers also replied to Nijman's tweet, including director and designer Brandon Sheffield. He revealed that he'd placed a rather random looking cow into the background of Necrosoft Games' Oh, Deer! while former Rollercoaster Tycoon 3 developer Andrew Gillett announced that booting up the game on Halloween will lead to some spooky menu music playing rather than the default track. Compared to the Uncharted 4 revelation, neither are likely to raise too many eyebrows, although even the latter is a little low key when compared to some of the other recently discovered Uncharted Easter eggs.

In Uncharted 4, for example, players can find pills from Weston pharmacy which features prominently in The Last of Us 2. In the first Last of Us game, players can find an old PS3 with a stack of Uncharted games nearby as well as a location that also features in Uncharted 3. The "Pelican" bar is almost identical in both games and in the latter, it even houses a newspaper clipping that references a deadly fungus; all but confirming that The Last of Us and Uncharted take place in the same universe. Whether the same can now be said for Assassin's Creed remains to be seen, though.

Uncharted 4: A Thief's End is out now, exclusively for PS4.

MORE: How Naughty Dog's Games Reference Each Other