Umbridge thought her little gesture had been very discreet.
With the light in her room so dim, she assumed Harry had not seen it.
But ever since Harry had injured his eyes during a Quidditch match and Madam Pomfrey had healed them, not only had his original shortsightedness disappeared, his eyesight had also become exceptionally good.
Later, his eyesight had kept improving, though he did not know whether that was due to the special ability in his eyes.
Apart from Ron, whose physical abilities were unreasonably good in every respect, and Krum, whose eyes already seemed as sharp as an eagle's, Harry had never met anyone with better eyesight than his own.
Later, the Black Man seemed to have taken away the ability in his eyes that allowed him to glimpse the future.
But his exceptional eyesight had not been affected at all. So Harry had seen the little gesture Umbridge thought so discreet with perfect clarity.
Taking the pumpkin juice from the old witch, Harry first pretended to thank her, then quietly sniffed it.
As the owner of the world's largest potions business, and one of Professor Slughorn's two favorite students since his return to Hogwarts-the other being Ron-Harry was only so-so at Potions theory, but quite skilled in practice.
He was one of the few students at school who could identify quite a few potions by smell alone.
Of course, if asked to brew them, he might make a complete mess of it.
Harry found the peculiar smell in his cup somewhat familiar. After a moment's thought, he remembered that it smelled a lot like Veritaserum.
It was not quite the same, though. There seemed to be some other things mixed into it.
Clearly, Umbridge or some other member of the Ministry of Magic had altered the Veritaserum