This appears as a thin 60 foot rope made from animal or creature hair. It will seem to be a magical Climbing Rope in all preliminary tests, and will display all associated powers, including the ability to snake upward and attach itself on the command of the owner, as well as the power to knot itself at 1 foot intervals on command.
The curse comes in later, out in the field, as it were, when someone actually needs to climb with it. When the character has climbed upward (or downward, if descending a sheer cliff or wall) over thirty feet, there is a 25% chance the knot will untie itself on the anchoring end, dropping the character. If the fall is only from that initial thirty feet, the climber takes 3d6 of falling damage. If the fall is from a greater height, the damage is commensurately greater. Even if the anchoring end was tied by hand, or clamped off somehow, the exact same chance of this happening still exists. The GM checks for this only one time per use; if the 1d100 roll is 26% or higher, the rope works as normal.
Most of the time it will work, in other words. Until it doesn't.