Well, to get them untangled you need only a longish, skinny piece of metal or
other hard-to-cut material
Step 1: Step 1
Step 2: Step 2
that chunk through the awkward loop (first tangle).
Step 3: Step 3
Note: hard to describe here.
Step 4: Step 4
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