But Ron, who did not appear to be listening to the toast, had already thrown the mead into his mouth and swallowed it.

There was one second, hardly more than a heartbeat, in which Harry knew there was something terribly wrong and Slughorn, it seemed, did not.

"--and may you have many more--"

"Ron!"

Ron had dropped his glass; he half-rose from his chair and then crumpled, his extremities jerking uncontrollably. Foam was dribbling from his mouth and his eyes were bulging from their sockets.

"Professor!" Harry bellowed. "Do something!"

But Slughorn seemed paralysed by shock. Ron twitched and choked: his skin was turning blue.

"What--but--" spluttered Slughorn.

Harry leapt over a low table and sprinted towards Slughorn's open potion kit, pulling out jars and pouches, while the terrible sound of Ron's gargling breath filled the room. Then he found it--the shrivelled kidney-like stone Slughorn had taken from him in Potions.

He hurtled back to Ron's side, wrenched open his jaw and thrust the bezoar into his mouth. Ron gave a great shudder, a rattling gasp and his body became limp and still.

....

They had done no more than satisfy themselves that Ron would make a full recovery on their last visit to the ward; now Mrs. Weasley seized hold of Harry and hugged him very tighty.

Chapters 18-19