She is the baby hippo who won over the internet when Cincinnati Zoo workers blogged about her health difficulties after she was born at least six weeks premature. 

And three-month-old Fiona treated her adoring public to a sweet video in which she opens her mouth wide in pleasure while a helper massages her gums.

In the 38-second clip, Fiona seems completely at ease and  closes her eyes in pleasure as the zoo worker rubs the inside of her mouth and even plays with her tongue. 

At her young age, Fiona has not yet grown the large teeth that hippopotamuses are known for. An adult hippo's incisors can reach up to 1ft 4in. 

The baby hippo is filmed happily splashing around in her training pool which will help her learn aquatic skills as her premature birth meant she was separated from the bloat (her herd of hippos). 

She had to be kept separate from her parents Bibi and Henry as her immune system was too weak to join the bloat. 

Fiona relied on a heater to keep her body temperature stable and the zoo built a special room where she could interact nose-to-nose with her parents while also being kept safe in her own germ-free environment. 

The zoo is also ensuring that she adapts to a hippo's aquatic life. 

Because hippos spend at least two thirds of their life in water, they must learn to hold their breath underwater and return to the surface for air.

However Fiona's diving responses - where she sinks underwater - endangered her life as she would not come up for air. 

As one blog post explained: 'Early on, she would exhibit dive responses while resting and sleeping, and they were often terrifying for the care staff to observe. 

'Fiona would close her nostrils (and often her eyes as well) and simply hold her breath for seconds and seconds on end. 

'During this time we could actually see the color draining from her face, the pink skin around her eyes and mouth turning white.'

But lolling in the training pool is teaching Fiona the vital skills of breath control and buoyancy so she can learn to live with her parents at the zoo's Hippo Cove.