A Real Bezoar Stone

Bezoars were first introduced into medieval Europe by Arabic physicians. Although doubts were sometimes cast over their properties, the demand continued well into the 18th century. Wealthy collectors spent considerable sums to acquire the best ‘stones’, which were kept in elaborate cases. Later, in The Half-Blood Prince, Harry put his learning to good effect. In his copy of Advanced Potion-Making, Harry had noticed the instruction, ‘Just shove a bezoar down their throats.’ He did exactly that when Ron Weasley drank some poisoned mead, thereby saving his friend's life.

‘Blimey, it was lucky you thought of a bezoar,’ said George in a low voice.
‘Lucky there was one in the room,’ said Harry, who kept turning cold at the thought of what would have happened if he had not been able to lay hands on the little stone.

Harry Potter and the Half-Blood Prince