All animals on Earth yawn, not just humans. It's an involuntary reflex that we do before or after sleep. It is usually associated with fatigue and boredom. Did you know even babies can yawn inside the womb? Aren't they sleeping already? This is Now You Know and in this video we'll find out why yawning is important for us.

So, why do we yawn? We don't know exactly but scientists say that our body needs it. We used to believe yawning helps bring in more oxygen to the brain and to exhale carbon dioxide, but this has been proven false.

A 2014 study has revealed that yawning regulates brain temperature. Whe we are tired or bored, our brain slows down because of lack of energy and stimulation which causes a temperature drop. We usually yawn around 20 degree celsius - the ideal temperature for brain and blood cooling.

We feel discomfort and face hearing issues during sudden altitude changes like in elevators and aeroplanes. Yawning relieves that by stabilising the air pressure inside our ears with the outside air pressure.

The fact that our heart rate increases during yawning tells us that it is meant to keep us alert when we are tired or bored. We know that it's true.

According to some researchers, yawning could be a language of its own. Before humans started speaking, yawning might have been a communication tool to convey boredom and tiredness or to show teeth to attackers.

We yawn when we look at someone else yawning. Even reading, hearing or thinking about yawning triggers it. Does this mean it's contagious? Yes it is and we don't know why. Some say it's an evolutionary response of social empathy and bonding, like when we cry watching someone mourn.

So how many times did you yawn while watching this video? Let us know in the "comments".