Why is a raven like a writing desk?

Riddle:
“This is an unusual paragraph. I’m curious how quickly you can find out what is so unusual about it. It looks so plain you would think nothing was wrong with it. In fact, nothing is wrong with it! It is unusual though. Study it, and think about it, but you still may not find anything odd. But if you work at it a bit, you might find out what it is.”
Classic Lateral Thinking Exercises, Top 100 Riddles of All Times, 2006.
Riddle Hint:
“What is the beginning of eternity
The end of time and space,
The beginning of every end,
And the end of every place?”
Riddle Answer:
What is the most commonly used letter in the English alphabet?

Puzzle1

GLaDOS: Have I lied to you?
[pause]
GLaDOS: … I mean, in this room?
GLaDOS, Portal, 2007.
Brainteasers, chocolate, and pastries are my péchés mignons. There, I said it!As a matter of fact, Antrim Escape is one of my favourite games, right after Portal. I personally believe that the best aspects of these games are the puzzles one is required to solve in order to unlock an achievement. Nevertheless, the main antagonist in Antrim Escape could have benefited from GLaDOS‘s cheerfulness, to say the least.After completing Antrim Escape 3, I found myself not only wishing that they made a fourth, fifth, and perhaps sixth one, but I also wondered whether there were any aspects of the game that I really enjoyed and could re-create and/or improve. As a result, here is my take on one of their cool mini-puzzles. Sadly I cannot say which one, because it might ruin the surprise.

Here are some hints:
  • The purpose of the game is to find the correct sequence
  • The number of blue circles increases after each correct click
  • The board is reset to two blue circles after an incorrect click
  • Don’t get frustrated, but a step back instead: you have seen this pattern before!