1. Hairy Harry's Hair
Sorry kids, hair doesn't grow back that quickly when cut. On average hair grows at a rate of 0.44 mm a day. A slight variance occurs depending on age but nothing that would equal the dramatic speed Harry experiences. It's possible he could have Hypertrichosis, AKA the 'Werewolf syndrome.' But even then it still wouldn't be at that speed.
2. Trolling the Troll
Since we already know that magic is just a lot of props and flash, two boys with sticks going up against a troll wouldn't stand a chance. If this was real life, that troll would have murdered the two boys and painted the bathroom with their blood.
3. Cat's Out Of The Bag
People can't turn into cats and then back to humans just like that. They can however use surgery to transform themselves into cats. Though that will take them many years and many different surgeries.
4. Snake In The Grass
Isn't it awesome when Harry talks to snakes? Wrong. It's a pocketful of lies. Snakes don't hiss to communicate, they use it to scare off potential predators. Harry hissing about is just a kid doing what kids do best, being stupid.
5. Sweep The Leg
I believe it is possible to ride a broom, if it has a clear means of propellant. The brooms in Harry Potter do not. Humans have yet to control gravity, despite decades of research. I'm afraid this notion of him flying deserves to go in the bin with the other sweepings.
6. Two Heads Aren't Better Than One
This is actually a real medical condition. The term is "Diprosopus" and is a horrible disease whereby a person or animal is born with a second face. The sad reality is that most born with such a condition don't live long. However, even if Professor Quirell managed to survive to that point, Harry touching him wouldn't turn him to ash. That's just nonsense.
7. The Fat Lady Sings.
Paintings don't talk!
I hope you've enjoyed this more realistic look at a children's movie. If Harry Potter was more truthful, he would have been sorted into Slytherin (which goes to show that stupid animatronic hat doesn't really work) and everyone would have eventually been dead at his hands. If you enjoyed this, tune in next time when I take apart The Green Mile.