The video has now gone viral on Twitter with more than three million views and shared more than 109,00 times. (Twitter Screengrab/ @satxjolynn)

In a shocking video doing the rounds on Twitter, a boy's reflection appears to move away faster than he does. 

The video shows the boy pulling faces in the mirror at his home in San Antonio, while his mother films him.

Shocked by what she saw, the mum sent the video on Snapchat with the words: 'Is it just me or did his reflection walk away quicker than he did?'

The video has now gone viral on Twitter with more than three million views and shared more than 109,00 times.

The video of the boy shows him sticking his tongue out before losing interest.  

But before he has even turned away the reflection has already disappeared, appearing to move faster that the child.

Twitter has since gone into a frenzy trying to understand how this is possible.

While one Twitter user said she didn't want to know the cause because 'that's how a little boy in scary movie starts', another said: 'I've never heard of a mirror that's got a .5 second delay.'

The original owner of the video posted it on August 20, @satxjolynn, said a day after posting it that the illusion was caused by a combination of the angle of the mirror, and the position she was sat in.