The River of Adventure by Enid Blyton

He only agreed to keep the snake as he knew it would not survive defenceless in the wild. Philip thought this very cruel, which is why Oola had his snake made safe a different way, one which Philip actually found just as cruel.

Those snakes, however had their mouths sewn up, to make them safe. It is Oola that presents Philip with the snake, after seeing him admire the snakes belonging to his uncle, the snake charmer. Well, it’s not actually poisonous, the poison ducts have been cut, rendering it safe, though it will not survive more than a few weeks. Philip has possibly his most unpleasant yet most useful pet in this story, a poisonous bargua. It’s then up to the children along with Tala and Oola to defeat Uma and his men, escape the underground temple and rescue Bill and Allie.

Raya Uma has laid claim to the treasure and is most displeased to find the children have found their way in through a back door.