The worst thing that happens to Slinkys is getting tangled, right?
Well, to get them untangled you need only a longish, skinny piece of metal or
other hard-to-cut material
Step 1: Step 1
Find the other tangle at one of the ends of the slinky.
Step 2: Step 2
Collapse the slinky from the first tangle to the other, then push
that chunk through the awkward loop (first tangle).
Step 3: Step 3
Stick the stick through as shown, then spin the slinky.
Note: hard to describe here.
Step 4: Step 4
If you still have a tangle on the end, then take the top-most layer and feed it below the true end.
Step 5: Summery
Note: Plastic slinkys don't get that extra tangle at the end.
If you don't have that extra tangle, it doesn't matter which end you collapse