How easily can a rat find its way into your toilet?
It sounds like an urban myth - but the latest video from the National Geographic may have you a little on edge the next time you visit the bathroom.
Rats in the toilet may not sound like an every day problem - but they are becoming more common in cities where rats find new ways out of the sewers and drains.
Recently in Belfast experts have warned that the number of rats in the city are on the rise.
The most recent video by The National Geographic has shown just how easy it is for rats to wriggle up the narrow pipes thanks to their flexible bodies - and find their way gasping for air in your toilet bowl.
Rats can swim for three days at a time and hold their breath underwater for three minutes.
The video explains how firstly the rats sneak into grates or manhole covers open to the street.
It says: "‘Residential sewer pipes feed into the main tunnel and a rat might consider this path an irresistible opportunity for exploration.’
"Its sharp claws allow the rat to scale almost any vertical surface, the rat is in the home's internal pipes going up.
‘Now it faces the biggest test, getting through the last few inches of the narrow maze like toilet pipes. Is this even possible?,’ the video says.
‘The underwater passage leaves no room for air. At a turn, the rat finds a pocket of air, just enough to help it push on to the end of the line.’
The National Geographic video explains how rat's ribs are hinged at the spine allowing it to squeeze through small spaces.
"If a rat can fit its head through an opening, the rest is easy because of its internal acrobatics.
"At the spine the ribs are hinged allowing it to effortlessly collapse."
But how do rats survive in so much water? Well where we think of rats as land animals they are actually expert swimmers.
National Geographic said: "Rats have incredible stamina they can tread water for three days straight and hold their breath under water for three minutes.
"This aquatic proficiency is the very reason rats became global travellers. Long distance swimming enabled them to hitch rides on boats and colonise new shores."