Ever wondered why humans have that vertical groove between the top lip and nose?
To be honest, it had never occurred to me to question it, but the answer is pretty interesting nonetheless.
The groove, known as the philtrum, is actually an important part of how our faces develop in the womb, as Dr Michael Mosley explains in this clip from the documentary series Inside the Human Body.
"It is the place where the puzzle that is the human face finally all comes together," he says.
"The three main sections of the puzzle meet at your top lip, creating the groove that is the philtrum."
The time-lapse video, created with data from special scans, shows how it all happens from between two and three months.
"If it doesn't happen then, it never will," explains Dr Mosley.
It all looks a little bizarre at first – you'll see the eyes moving from the sides of the head to the front – but it's fascinating stuff.