Harry and the others had actually "accidentally" learned from Hagrid long ago how to deal with Fluffy, the biggest obstacle at the entrance to the Fourth-Floor Restricted Area.
So before opening the door, Harry took a Music Box he had prepared long ago from his pocket and wound it up. A lilting melody began to chime.
Hermione still reminded them.
"Are we really not going to tell any other professors?"
Harry shook his head.
"No one will believe us. Professor McGonagall even warned us not to make accusations lightly. She said this was a very serious allegation."
Draco did not particularly care. He did not actually believe Harry's suspicions about Snape at all; he had only come along to back Harry up.
"Alohomora!"
Harry said no more and used the unlocking spell to open the door.
An enormous Three-Headed Dog greeted their eyes. Even lying on his belly, he reached the ceiling.
All three of his heads were ferocious, with exposed fangs. But the Three-Headed Dog was already asleep, thick, foul-smelling drool still dripping from his mouths.
A white Harp as tall as a person stood in the room, playing a tune on repeat.
"Snape really has gone down. Come on, hurry!"
Looking anxious, Harry put away the Music Box, stepped forward, and began hauling on one of the Three-Headed Dog's massive, fleshy paws.
Draco and Hermione went over to help. Together, the three of them laboriously moved the huge paw aside, revealing a Trapdoor.
The Harp did not suddenly stop playing in some melodramatic twist.
Harry had been here the previous year and had nearly died along with Ron in the Devil's Snare below.
He had told both of them roughly what was down there. After opening the Trapdoor, the three jumped down one after another without hesitation.
A