Neville chuckled. Luna turned her pale eyes on him instead.

Neville chuckled. Luna turned her pale eyes on him instead.

‘And I don't know who you are.’

‘I'm nobody,’ said Neville hurriedly.

‘No you're not,’ said Ginny sharply. ‘Neville Longbottom—Luna Lovegood. Luna's in my year, but in Ravenclaw.’

‘Wit beyond measure is man's greatest treasure,’ said Luna in a singsong voice.

She raised her upside-down magazine high enough to hide her face and fell silent. Harry and Neville looked at each other with their eyebrows raised. Ginny suppressed a giggle.

The train rattled onwards, speeding them out into open country. It was an odd, unsettled sort of day; one moment the carriage was full of sunlight and the next they were passing beneath ominously grey clouds.

‘Guess what I got for my birthday?’ said Neville.

‘Another Remembrall?’ said Harry, remembering the marble-like device Neville's grandmother had sent him in an effort to improve his abysmal memory.

‘No,’ said Neville. ‘I could do with one, though, I lost the old one ages ago.... No, look at this....’

He dug the hand that was not keeping a firm grip on Trevor into his schoolbag and after a little bit of rummaging pulled out what appeared to be a small grey cactus in a pot, except that it was covered with what looked like boils rather than spines.

‘Mimbulus mimbletonia,’ he said proudly.

Harry stared at the thing. It was pulsating slightly, giving it the rather sinister look of some diseased internal organ.

‘It's really, really rare,’ said Neville, beaming. ‘I don't know if there's one in the greenhouse at Hogwarts, even. I can't wait to show it to Professor Sprout. My Great Uncle Algie got it for me in Assyria. I'm going to see if I can breed from it.’

Harry knew that Neville's favourite subject was Herbology, but for the life of him he could not see what he would want with this stunted little plant.

‘Does it—er—do anything?’ he asked.

‘Loads of stuff!’ said Neville proudly. ‘It's got an amazing defensive mechanism. Here, hold Trevor for me....’

He dumped the toad into Harry's lap and took a quill from his schoolbag. Luna Lovegood's popping eyes appeared over the top of her upside-down magazine again, watching what Neville was doing. Neville held the Mimbulus mimbletonia up to his eyes, his tongue between his teeth, chose his spot, and gave the plant a sharp prod with the tip of his quill.

Liquid squirted from every boil on the plant; thick, stinking, dark green jets of it. They hit the ceiling, the windows, and spattered Luna Lovegood's magazine; Ginny, who had flung her arms up in front of her face just in time, merely looked as though she was wearing a slimy green hat, but Harry, whose hands had been busy preventing Trevor's escape, received a faceful. It smelled like rancid manure.

Neville, whose face and torso were also drenched, shook his head to get the worst out of his eyes.

‘Sosorry,’ he gasped. ‘I haven't tried that before.... Didn't realise it would be quite so... Don't worry, though, Stinksap's not poisonous,’ he added nervously, as Harry spat a mouthful on to the floor.