Pharyngeal airway illusion
Your patient is getting obstructed. You want a large airway to insert into his oropharynx. So which airway below is bigger ?
Most people will see that the lower airway is bigger.
In reality, they are both exactly the same size. The fixed size red rectangle shown below shows you this.
Tracheal tube illusion
Your patient is still obstructed. You decide to intubate. You want a long tracheal tube. Which tube below is longer, the horizontal or vertical one ?
Most people think that the vertical one is longer than the horizontal one.
However, as the animation below shows you, both tubes have exactly the same length.