Non-animagus animal transformations / Sirius and Dementors

[Torsten]

No: HPFGUIDX 49962

There's a lot of talk about animagi, but what about normal wizards transforming into 
animals? We're given several examples of wizards turning objects (Cedric in GoF), each 
other (The Amazing Bouncing Ferret; mention of a student turning his friend in a 
badger; canary creams) or themselves (Krum) into animals. It seems like transforming 
oneself is the most difficult, since Krum's shark-transformation was incomplete, but it's 
possible. The only advantage of animagi is apparently that they don't need a wand 
and/or spell to change.

Now, in PoA, the Ministry and the Hogwarts staff think of all kinds of safety 
measures - why does no one expect Sirius entering the grounds in animal form? They 
don't know he's an animagus, but he's a fully-trained, brilliant wizard, he could 
transform in the normal way. The spell might require a wand, but it had to be expected 
Sirius somehow got one, either by theft or from a fellow DE. Everyone's on alert, but 
no one wonders about that big dog, not even when it watches Quidditch? Strange.

Next, just why is Sirius overwhelmed by the Dementors' powers at the end of PoA? 
He made it through Azkaban, so he's kind of used to having many of them around, and 
he says it didn't affect him there because he wasn't really guilty. That hasn't changed, 
and now he's got even more that should give him purpose and strength, catching 
Pettigrew and protecting the kids from Lupin. Why did he change back into human 
form in the first place? He either lost his wand or is unable to summon a Patronus, so 
he's only making things more difficult for himself by taking human shape. It would be 
easier to escape the Dementors as a dog

Torsten