For the professors, collecting materials in the Forbidden Forest was hardly unusual.
When Remus had served as Hogwarts' Defence Against the Dark Arts professor, he would go into the Forbidden Forest to find swamps and catch Sinkpunks and Kappas from them.
The Boggarts he used in class were also caught in abandoned old rooms of the castle.
Professor Sprout would occasionally come to the Forbidden Forest to dig up wild vegetables or collect manure. As for Hagrid, the magical creatures he showed the young wizards in class were all native species from the Forbidden Forest.
The same went for Snape. Some of the materials used in Potions Class were gathered by him deep within the Forbidden Forest.
For the professors, this was simply part of their daily work.
Following a secluded trail, Snape led Malfoy and the others through the towering trees with difficulty for about an hour before finally arriving at the edge of a vast swamp near the Black Lake.
Thick miasma floated above irregular puddles, twisting into bizarre shapes in the breeze.
The rotting carcasses of some animal floating in the water filled the area with a powerful stench of decay.
Malfoy looked around and spotted faint orange-red glows in the hazy mist. The lights pulsed like hearts, giving off an enticing allure.
After a brief moment of confusion, Malfoy immediately became alert.
He realized they were Sinkpunk traps, meant to lure lost travelers into the swamp.
"What do we do?"
Malfoy raised his head and asked Snape. His voice also woke Pansy, Theodore, and Blaise, who had been briefly entranced.
Snape took several large glass bottles from his robes and handed one to each of them.
"Do not go deep into the swamp. Stay by the edge."
"How are we supposed to find leeches, Professor Snape?"