These illusions are all effects. Easy to create, fun to edit and there is no limit to the cool optical illusions that can be created.
Create a shape. Solid fill, no stroke
Add an effect. Effect > Distort & Transform > ZigZag. Also try other Effects, roughen, pucker, bloat.
With the Effect applied, choose Object > Expand Appearance.
This is the shape after the Expand Appearance.
Copy and Paste the shape in place. Scale the pasted shape much larger. and center both shapes on each other.
Select both shapes. Choose Object > Blend > Blend Options. Set the Spacing to Specified Steps. Set the number of steps to 20. Click OK. There will be no visible result from this step until the next step.
Select the blended shape and choose Effect > Pathfinder > Exclude. Do not use the Exclude from the Pathfinder panel, it will look the same but the results will not work.
Select the shape, then double click on the outside shape to enter into Isolation Mode. (You should see a gray bar across the top of the document to indicate Isolation Mode. )
Choose Effect > Distort & Transform > Transform. Click the Preview button. Set the angle to rotate the outer shape. The more you rotate, the more twist will appear.
You can try these effects with any shapes.
The star can create a dimensional look to the shapes.
With a square, apply a Pucker effect. Then follow the steps to create the Exclude effect.
This shows when you rotate the isolated outer shape
You can also isolate the outer shape and move the shape to create a tube effect.
With the outer shape isolated and selected, you can adjust the Corner Widgets and create a cool effect. Try it with any shape you can imagine.