Though the Occamy was widely known for its serpentine body and birdlike wings, its name came from its eggs: a nonmetallic substance that looked very much like silver. Like pearl powder, bone, and fish bones, it could be ground into powder and was an essential ingredient in Felix Felicis.
The Hogwarts Occamy population did not merely produce eggs that had become extremely fragile and lost their metallic sheen. The young Occamies they produced also died prematurely, or could not even hatch at all. That was why Lockhart had taken Occamy eggs for his experiments and made shampoo.
Around 1986, Severus somehow acquired a batch of premium-quality Occamy eggshells. He proudly told Filch and Madam Pince about them, but somehow, two sixth-year students found out. They stole the eggshells and used them to make Felix Felicis.
How difficult could Felix Felicis be? The troublesome part was gathering the ingredients. Those two students insisted that their potion had failed only because they did not have ingredients good enough. As long as they found better materials, they would definitely succeed.
By the time Filch's cat, Mrs Norris, found them, they had already ground the Occamy eggshells into powder and added them to the cauldron. When Snape arrived, the Felix Felicis had turned into something like tar. His fury was so great that people suspected he might pour the entire cauldron of potion down the students' throats.
This time, Albus unusually took Severus's side. He did not expel the two students, but from the second half of their sixth year until graduation, they served detention under the Potions professor and endured endless sarcasm and mockery. There was a way for them to escape all that: they could leave school. After all, they had already passed their Ordinary Wizarding Levels and met the standard of