Some readers may find parts of this story disturbing.

On a counter at the popular Mayorista market in Lima, stand two small, glass aquariums, containing dozens of toads and frogs. The frogs are from the Andes mountains, and some of the species are endangered. The stallholder works quickly, taking orders from a stream of customers who perch on stools or stand watching her work.

Making a "frog shake" takes a few minutes. First the stallholder grabs a frog from the tank. She cuts its neck with a knife and skins it as easily as if she is peeling a banana. Then she puts it into a pan on a small stove with some liquid. Next the bubbling concoction is poured into a liquidiser with the other ingredients - powderedmaca, a medicinal Peruvian root, vitamins, fruit and honey. The stallholder stops the blender and tastes the thick green mixture, her face a picture of concentration. She spoons in more honey, gives it a final whizz and pours it into a tin jug.

"It's very good for anaemia and for chest complaints," says a customer. It is also known as a kind of Andean Viagra. "It's good for that too," he agrees. "But for anyone who's ill, if you take it three or four times a week, you will feel better very quickly."

The amphibian "smoothie" originated among indigenous communities in the Andes, but its popularity has spread. Here, it costs five Peruvian soles - just under $2. "I sell maybe a 100 a day," the stallholder says. And she is well aware some of the frog species are under threat. "We all know that, but well… When they disappear, they disappear. But while we have them, we can help people with this drink."

A couple approach the stall with a small lidded, plastic box. They buy two frogs to take away. The woman explains she will make her own frog shake at home following an old family recipe, and use it to treat a lung complaint.

The stallholder has been fined several times for selling the frog drinks, but she has continued to trade - and customers continue to believe, without any scientific evidence, that the drinks benefit health.

(An excerpt from BBC's 'The country that blends endangered frogs')