A conceptual Illusion
The illusion presented here was inspired by the suggestion of Cupcake. I will not duplicate the exact puzzle because I have a feeling that Cupcake may already have a good solution and is just waiting for a good time to reveal it. Instead, I present somehwat different illusion. Another advantage of this illusion is that it emphasizes some of the weaknesses and strengths of the "slip and Stick" methodology.
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The parts used in the concept illusion look like the three parts shown below.
The parts used include sticks, elbows and slips. The number of parts used is shown in the table below.
Part Amount
Elbows 4
Sticks 4
Slips 8

Each of the pictures below shows the parts partially assembled. Each picture shows a different view of the same parts. One stick is inserted into one elbow and held in place with one slip and an additional slip is on the opposite end to aid in assembly.
These partially assembled parts are viewed from the top, bottom, outside and inside.

Imagine a small robot placed in the circle on one of the elbows: The robot can start on any circle. The robot must follow the green line. The robot can go forward but can not go backward and can not retrace any path once it is traveled.
The First Task:
Imagine a method to assemble the parts so that the robot will start and in the same circle no matter which circle is chosen.
The Second Task:
Determine the following: Which starting circle gives the shortest path. Which circle gives the longest path. How many different paths are there (one path can include more than one circles).
I will present one solution in about a week on my web site.