A mother has described the horrifying moment she popped a giant growth on her son’s knee - only to discover a black sea snail inside it.

Rachel Franklin, of Orange County, California, noticed her seven-year-old son Paul’s knee had swelled to the size of an orange.

She had previously taken him to the doctor, who said the growth was a staph infection, prescribed antibiotics and told her not to pop it.

Rachel Franklin has spoken of her horror when she popped a giant growth on her seven-year-old son Paul’s (centre) knee and discovered a black sea snail inside

Recalling the incident, she said she had previously visited the doctor, who said the growth was a staph infection, prescribed antibiotics and told her not to pop it

The snail had been growing in the tissue above Paul’s knee. It was identified as a littorina scutulata, a type of sea snail that can survive in a wide range of temperatures and waters

But when the swelling turned black, and began oozing pus, she decided to defy the orders and drain it.

However after popping the wound, she was horrified to a strange black object inside the wound - which she initially believed was a piece of rock.

‘I’m peering at this object and it has a strange look about it,’ she said during an episode of Monster Inside Me, which will be aired on the Discovery Channel next Wednesday.

‘I realised it wasn't a rock. It has whirls on it.

‘I turn it over and I think - I might have laughed out loud. I said, “Paul. This is a snail. It’s a freaking snail.”’

While many would be disgusted at having a mollusc inside their body, Paul simply said it was ‘cool,’ his mother added.

The snail had been growing in the tissue above Paul’s knee, with pus and black-looking tissue emerging as the body’s immune system detected a foreign invader.

The programme reconstructs the moment, in 2013, when the snail was discovered.

Biologist Dan Riskin explained that littorina scutulata snails can survive for weeks in different temperatures and salt levels. The tissue below the skin in the body mirrors these harsh conditions, he said

The snail was found to be a littorina scutulata, a type of sea snail that can survive in a wide range of temperatures and waters, biologist Dan Riskin explains in the programme.

‘It can even live outside of water for several weeks by retreating into its shell,' he said.

‘It lives in the harshest intertidal zones and can survive for weeks in a wide variety of temperatures and salt levels.

I said, 'Paul, this is a snail. It’s a freaking snail' Rachel Franklin

‘The subcutaneous tissue of the human body mirrors the harsh conditions where sea snails normally survive.’

Paul's father, Ken, believes the little animal made its way into his son's leg after he fell onto a nest of snail's eggs at the beach in Spooner's Cove, California.

Paul, who describes the whole incident as 'crazy' has since named the snail Turbo.

The new series of Monster Inside Me is premiering next Wednesday (4th November) on Discovery Channel in the UK.