Sirius's attack on Ron; how Sirius got in

[dicentra_spectabilis_alba]

No: HPFGUIDX 36120

Been perusing PoA with a fine-toothed comb and came up with a question
and an observation:

Sirius shows up with a knife and slashes Ron's bedcurtains AFTER
Scabbers fakes his own death. Sirius later says that Crookshanks told
him about the faked death. So why go looking for Scabbers in Ron's bed
at that point?

Also, after the Shrieking Shack scene, when the Trio are in the
infirmary and Dumbledore finally manages to kick everyone out
(including a comically irate Snape), Hermione and Harry hit Dumbledore
with a barrage of statements, the last one being "...Pettigrew
attacked Ron, it wasn't Sirius..."

Since I had the aforementioned question in my head, I wondered if Ron
had seen Pettigrew that night and mistaken him for Sirius. But then I
realized that the "attack" refers to what happened just as Lupin
transformed into a werewolf--Pettigrew gets hold of Lupin's dropped
wand (***note to those who wonder about lost wands: apparently, they
do get dropped when wizards transform***) and blasts Ron and
Crookshanks before Harry expelliarmuses him, he transforms into a rat,
and disappears into the grass.

What's interesting is that Hermione or Harry (can't tell who said it)
would fixate on *that* attack, conveniently forgetting that Sirius did
in fact attack Ron and break his leg.

And Cindy, I don't think Sirius used the witch's hump to get into the
castle, either. He probably exited through the willow and snuck in
through whatever passage Crookshanks was using to get out. Or he
waltzed in the front door as a dog and the doors, having been taught
to look for Sirius Black, didn't know the difference.

--Dicentra, who is amazed and not a little pleased that details still
turn up no matter how many times she reads PoA