When a crocodile grabbed her sister, there was only one option for Georgia Laurie - she punched it in the face.
The 28-year-old twins were swimming in Mexico when Melissa was dragged underwater by the reptile.
The sisters, from Berkshire, were in a lagoon near Puerto Escondido, on Sunday, when the attack happened.
They'd been travelling, volunteering and working in animal sanctuaries - their sister Hana tells Radio 1 Newsbeat.
'She just started hitting it'
Both sisters, who live in Berkshire, are now in hospital in Mexico - and Melissa is currently in an induced coma, because of worries of infection from the injuries she sustained.
While they were swimming, Melissa disappeared under the water and Georgia had been trying to find her.
Crocodiles try to drown their victims.
"Georgia found her unresponsive and started to drag her back to the safety of a boat," says 33-year-old Hana from her home in Alton, Hampshire.
"She dragged her back as the crocodile kept coming back for more - so she just started hitting it.
"She'd heard that with with some animals, that's what you've got to do."
Hana says Melissa was thrown about like a "rag doll" by the crocodile.
"Luckily, her super-badass twin sister was there to punch it repeatedly - as it came back about three times - to try and save her."
Doctors are concerned about the water the sisters were swimming in, as well as anything that might have been passed on from the crocodile's mouth and teeth.
Melissa has water on her lungs and possibly a punctured lung as well. She's currently receiving help to breathe.
"Both Georgia and Melissa are on heavy doses of intravenous antibiotics, so we're really hoping that if any infection does develop that they'll be able to catch it really quickly," says Hana.
'Her adrenaline kicked in'
Hana says Georgia is an experienced diver, but was "so frightened" when she came face to face with the croc.
"Thank goodness she's had that training. She said her adrenaline kicked in and she knew what to do."
Their dad is in contact with the British Embassy in Mexico to try and get support for his daughters, but Hana say it's stressful being so far away from her sisters.
Their concern now is how they'll pay for Georgia and Melissa's hospital stay - they're not sure yet if their insurance will cover the treatment they're receiving.
But they've been able to speak with Georgia on WhatsApp and she's made FaceTime calls from her hospital bed.
"Georgia's getting sporadic updates from the doctors as they come in to see her, about Melissa's condition. It's difficult," says Hana.
"She is so brave and I think she's still in shock. But I just had to tell her how proud I was of her.
"I'd have one less sister if I didn't have such an excellent other sister."