Disposable, microwavable container
Pure acetone about 1 tablespoon
Proper Ventilation (go to a room with a ceiling vent like a ventilator above your stove or the air vent in your bathroom (it stinks)
Speaking of stinky things here is a song for the occasion. Mom used to sing this when she was a kid.
Take your disposable microwaveable container and add Styrofoam pieces into it (we used a plastic bowl) Then add the acetone a little at a time and stir with a spoon or use your hands if you can handle the goo. Shape into a ball. Place into the microwave 30 seconds at a time, until you get the desired brain shape.