This is going to get technical, but bear with me. We started with 100 ml of Science Powder in each Science Vessel. Then we added a further 100 ml of Science Water and used our Science Stirring Tools to agitate the components until we developed the non Newtonian liquid we were after.

From there, it became significantly less scientific as the oobleck/goo/gack went everywhere. We poked, prodded, and played. Someone even got it on his nose. And because it was just Science Powder and Science Water it cleaned up really easily, though watching the "solid" bits of oobleck "liquify" in the garbage can was eerily reminiscent of Terminator 2.

John Connor? Next house over. Have a nice day.