What about the Door(that wasn't at the end of the tunnel)?

[snow15145]

No: HPFGUIDX 99606

Alla said
I am 99% sure that Jo said that in her last chat in march. I don't
have a link right now, but I think the question and answer sounded
something like that (very paraphrased):

"Why Sirius sent Snape to the Shrieking Shack ? because Sirius
loathed Snape and feeling was entirely mutual. You will find out more
about the reasons in a due course".

Again, it is very paraphrased and I could be wrong, of course.
Snow replies:

Nice memory Alla! I think this is the part of the chat you were 
referring to:

Kyla: What made Sirius decide to send Snape to the Willow?
JK Rowling replies -> Because Sirius loathed Snape (and the feeling 
was entirely mutual). You'll find out more about this in due course.

Snow-aka Kathy King