It's a gizmo that pulls double knit thread back into the fabric when it snags. You can still buy them in the notions department but they are smaller now and have plastic handles. They are in the same section as seam rippers. They work really good too!

I have a knitting machine and the end looks just like the needles used for it. So I would say it is used for picking up dropped stitches in knitting.

Yep, that's it!

Jan in VA

I think this is the right answer. Too small for a latch hook for wool rug hooking.

Why does it have a spring on it?

That's what I thought! That piece that sticks up may just be handy for positioning the hook end. Still think it's an odd little gizmo...

I think it is for when you get a snag in a sweater you use that to pull it through so the snag isnt there anymore.
But at first look, I thought it was for a latch rug hook, but it has that spring looking thing and I don't think that the latch hooks have those at least none that I have ever seen.

The small ones are for pulling snags through to the inside of knitted cardigans and jumpers and for pulling the final threads through the back of the stitches in tapestry and embroidery. The big ones are used for making rugs - to pull the wool through the canvas and knot it. They are called latch hooks and I have a variety of them and have use them for all of the above. My mum made all of the rugs in our house using the tools - I got bored after one!

It is a nit-picker, used for pulling snagged stitches to the back in a sweater

It is for catching the dropped knit stitches. I use my great grandmothers when I knit on the machine.