question about crookshanks

[ac4lb]

No: HPFGUIDX 185766

I know this is off the regular topic being discussed at present but I
have a question. In POA what is the relationship between Crookshanks
and Sirius Black in his dog form? Did I miss information in the book
that explained that somewhere? Crookshanks and Sirius are always
looking for scabbers but then Harry sees them walking together on the
castle grounds one night. Anyone have any clue if there's something
about Scabbers I missed?

Kathy