Mix the flour salt and cocoa powder together in a bowl.
Pour in the water, oil and stir until the playdough starts to form.
Allow to coil a little and then turn out and knead.
Add in the 4 - 5 drops of glycerin and knead further.
Continue to knead until you have a smooth consistency to your playdough.
Notes
This playdough will store for a week at the most in an air tight container so that it doesn't dry out.Although taste safe the quantity of salt will make it dangerous for pets and if ingested seek medical advise for pets or children.