This cat toy rolls and wobbles erratically, and is full of catnip!
It is unsymmetrical, and the shorter end is almost solid to add weight and balance the toy so it will roll. As it rolls, any sideways wobble changes the diameter of the "wheel", so it rolls, turns and wobbles in a chaotic manner.
The catnip is added by pausing the print, so the catnip is trapped inside. Print it with the perforated end down, and pause at a Z height of about 55mm. Add the catnip, using a funnel if necessary, and tamp it down gently before resuming the print.
Use dried catnip which has been lightly moistened. This is for two reasons: to keep the catnip from being blown around by the extruder fan, and to keep the catnip from being baked too dry over the heated bed, Before starting the print, spread your dried catnip on a piece of scrap paper, and lightly spritz with clean water using a spray bottle. Don't get it soggy, just lightly damp. I didn't measure the catnip, but I think I used about a heaping tablespoon or so for each toy.
Remove the print promptly so the catnip does not dry out too much in the heated environment of your 3D printing area.
Print with any rigid material which can render the 1mm holes. I used PET-G for mine (specifically, nGen and colorFabb-HT) but PLA would also be a good choice. (A material with a stronger odor, like ABS, might not be to your cat's liking.) Use your standard print settings for your material. To make it balance properly, try an infill of about 75%.
I used a 0.5mm nozzle, 0.25 layer height, 1mm shell thickness and 1.25mm top and bottom thickness. However, whatever settings you use for a "standard" part will probably be just fine. No supports or post-processing are necessary.
Designed with Autodesk Inventor. I used Inventor's Center of Gravity tool to balance the model, although I had to fudge it a little to account for the weight of the catnip.