Wonderfully and poignantly crafted. The word 'little' may or may not mean a kitten or young cat, of course, but that's another reading I can make. What I get from 'rusted' is that this is both a very long time ago, even decades, and perhaps the collar was amongst the remains of a relative passed away recently.
Whatever reading is correct, I personally get a lot from the poem.
I'm sort of a cat person, mostly because they adopt me:
how come this cat knows
my midnight reasons
Raindrop, A Journal Of Short Form Poetry (Issue 1, 2013)
It is an emotional ku. Dan has crafted the poem with vivid images. The word phrase,'rusted' speaks a lot. Perhaps there is no liberation and freedom in the life of the cat. Its voice is also made silent. The haiku renders a meaningful message. A brilliant creation by Dan Curtis.
In contrast, the following haiku portrays differently.
every one crosses
also a cat
Pravat Kumar Padhy
Bottle Rockets #27, August 2012 (Ed. Stanford M. Forrester)