1. Go to Youtube.com
2. Play any video you want
3. Pause it
4. type (keyboard) 1980
5. That's an easteregg!

Unlike those colorful eggs associates with the Easter bunny which we all know, when talking about Easter eggs in technology products they mean a hidden little secret that are undocumented and many time, no one except for the developer knows that they are included in the product, some may be considered as cheats.

Easter eggs go far into the past but let's take a look at Atari (which for most of this blog readers is way back).
Atari didn't allow developers to credit their names, so they hid it in places hard to get and which required a special navigation to get to.

Atari Easter Egg (hidden developer's name).

Even good old Google has more than a few Easter eggs, here's just a few for you to try:

• Google the term: do a barrel roll.
• Search for atari breakout on Google Images.
• A geeky one would be to search for recursion and having Google ask: Did you mean "Recursion".
• Google for "binary" and get the number of results in binary instead of decimal.

The developers of vogue, have included an Easter egg that by pressing a specific key combination, shows a raptor with a fashionable hat running at the bottom of the screen.

www.vogue.co.uk - try "Up, Up, Down, Down, Left, Right, Left, Right, B, A"

You should definitely look for Easter eggs, one company hid a 1000$ bounty in their EULA (End user license agreement) - that thing which you always press "Yes, I read it", it was found only 7 years later (!!!).

An example from facebook who has its own Easter eggs:

Facebook has not skipped it's own Easter eggs - English Upside down.

Here is a mobile Easter egg found on safari browser on iPhone:

Speedtest.net's mobile app has an Easter egg dedicated to the cat which the company "Ookla" is named after:

So why does having Easter eggs in your product important?
First, it's a motivator for the developers.
This is the developer's unique footprint in the product that he is developing, all other stuff comes from the PM. It allows creativity and motivation to thrive and involves the important element of FUN.
Secondly, for the user of your product, finding these Easter eggs is (did we already mentioned) fun.
The element of discovery is amplified, and the satisfaction of finding one is so great as you find something most users have no idea of.

If you found any cool Easter eggs, please share them with the readers in the comments - Thanks!

Emotional Contagion:
Yes, some emotional expression is contagious.
Ever wondered why you yawn when you see someone else yawn?
This behavior is subconscious and since from an evolutionary  point of view we are a part of a herd, it is meant to send a social message.
Smiling has a similar effect, and here is where emotional contagion comes in handy in your product:
Just like the explanation above, when we see someone smiling at us we smile back sometimes uncontrollably.
When we smile our body releases serotonin, dopamine and other "feel-good" indicators.

When you use a smiling avatar or image, you contribute to the user's positive feelings and actions.

Obligation - Public commitment:
Did you ever promised yourself "I'll start a diet tomorrow" ?
If you did promise but didn't keep it, think now whether the outcome would have been different if you said it in public - most likely yes.
When we commit to something in front of others we are way more likely to inspire for completion of this commitment.
If a user shares a good thing about your product to facebook, and he gets likes showing that people paid attention to this piece of his, he is most likely to stand behind his statement in the future.

Authority and Likes:
We highly regard opinion and reviews made by specialists and people we like.
If I see a Mashable good quote about a product, I am likely to accept this quote as opposed to a user which I am not familiar with.
Having many reviews, testimonials, "as seen on...", etc. will gain you credibility and users will feel confident.

Scarcity:
Less is more.
We instinctively assign greater value to things which are in low availability due to the fear of losing them.
Good examples are: 4 last rooms available (in a hotel), 9 seats available on a specific flight, etc.
A good way to leverage this concept is to offer membership program.
An interesting implementation can be seen with Gilt.com, where offers are available for a specific time period, Premium users don't get a discount nor a free item, they get 15 minutes head start for auctions.
Yes, that's right, so think about scarcity next time you want to push sales.

Options:
We think we like to have many options to choose, we don't.
When building a flow in your product, don't give the user too much choice, he should have as least options as possible.
Too many options might cause confusion and inability to reach a decision, ending up in churning.