The scream he heard was his mother's as she was killed by Voldemort. This was his worst memory and the
Every time Harry is confronted with a Dementor, he hears the screams of his mother as she is murdered by Lord Voldemort. A horrific memory to hear... He hears this moment because Dementors feed upon happiness and cause depression and despair in anyone near them. They make people relive their worst memories.
Because dementors seek to suck out the souls of their prisoners, it's plausible that they are especially drawn to Harry because — as it is revealed in the last book — he actually possesses a fragment of Lord Voldemort's soul as well.
Harry has the magical ability, therefore his mind identifies the snake voices and automatically translates them, making it seem like he's hearing a person speaking. The same happens when he speaks in Parseltongue; he thinks he's speaking English, but snake voices come out of his mouth.
Description. When the Dementor's Kiss is performed the Dementor will pull back its hood, clamp its jaw around the victim's mouth, and consume his or her soul. The Dementor's Kiss is generally considered to be a punishment worse than death.
J.K. Rowling told us, 'the mood-enhancing properties of chocolate are well known in both the Muggle and wizard worlds. Chocolate is the perfect antidote for anyone who has been overcome in the presence of Dementors, which suck hope and happiness out of their surroundings.
It had administered its fatal Kiss to Barty Crouch. It had sucked his soul out through his mouth. He was worse than dead. Shortly after confessing his traitorous deeds disguised as Mad-Eye Moody, the tortured Barty Crouch Jr had his very soul sucked from him.
They muted Harry's scream when Sirius died because it was so heartbreaking that Helena Bonham Carter (Bellatrix) and Emma Watson (Hermione) cried. It was too sad to watch, so they muted the scream.
It's pretty much general consensus that the scream Harry hears while on the train back to Hogwarts in The Prisoner of Azkaban is that of his mother, Lily, just before she is murdered by Voldemort.
He has grown afraid of Harry's connection to Voldemort. Perhaps Voldemort, knowing Dumbledore's love for Harry, would possess Harry and provoke Dumbledore to kill him. So, Dumbledore attempted to avoid Harry throughout Book 5 for Harry's own good.
Death Eaters spread despair, allowing the dementors to feed on it and breed. The Dementors take care of the Death Eaters enemies, taking their souls, and demoralizing the rest of the population. It's mutually beneficial to both of them. This is why the Dementors joined Voldemort.
A theory posted on Reddit suggests Dementors were drawn to Harry because they could sense the piece of Voldemort's soul living in him. Harry is an “accidental horcrux”, created when the killing curse casted by Voldemort backfired, fragmented his soul, and sent a piece of it to Harry's body.
The Dementors made his inner feelings of hurt and abandonment come to life, along with bringing back his worst memories. As mentioned by Remus Lupin, Harry's true fear was fear itself, which the Dementors projected. The creatures forced him to feel the defeated mentality inside of him that he generally pushed down.
Narcissa Malfoy's Very Dangerous Lie
But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
Dementors personify depression
The soul-stealing dementors, creatures that suck hope and happiness out of anyone they're near, first appear in Prisoner of Azkaban. According to Rowling, they're a physical manifestation of what it's like to experience depression.
Lupin explains that Harry is more deeply affected because Dementors work by extracting good memories, leaving nothing but the bad recollections, and Harry has a much grimmer history than anyone else.
When Harry's mom sacrificed herself to protect him, she created a defensive barrier for Harry with her love. Voldemort cannot touch Harry directly because of this magic. He cannot harm Harry at the Dursleys because Lily's blood (Petunia being her sister) gives him protection there.
Solution. There were monkeys racing all along the tracks. One of the monkeys tried to snatch a banana that a girl had in her hand. So she screamed.
90% here thinks he laughed because he simply lost it, he had a mental breakdown. Though some people believe Wormtail put a laughing charm on him after he blew up the street to make him laugh uncontrollably.
Dumbledore didn't know for certain that Sirius was innocent, and for the most part, it didn't matter. Sirius wasn't useful. Also, see Remus - Dumbledore saw no use for him, so didn't help him.
Because Dumbledore had no idea that the Potters changed Secret Keepers from Black to Pettigrew. Therefore, Dumbledore had no reason to believe that Sirius was innocent and no reason to try and help him.
Reproduction. Dementors breed by surrounding themselves with large amounts of a special fog which they exude. New individuals, already fully formed, will gradually congregate from the mist.
The latter would mean that the person who got kissed is literally trapped in the Dementor's body while the victim is still alive, which is likely why some call it a fate worse than death (assuming a Dementor's interior is as bad as their appearance).
Hermione Granger received one from Professor McGonagall in 1993, so that she could attend more classes in her third year than time would allow.