Disgusting...cat spit. But very cool for Halloween!
Pour out and smooth out some baking soda onto a plate, pie pan or cookie sheet.
Give your child a teeny cup of vinegar and drop a few drops of food coloring into the vinegar. Let your child use an eye dropper, or a syringe to suck up a little colored vinegar. You can even teach your child how to dip a straw into the vinegar and cap the straw with a finger to trap a little vinegar in the straw.
Release the little bit of colored vinegar into the plate of baking soda... and observe!
Inevitably, the question was asked, "What happens if I pour the baking soda into the vinegar cup?"
Hissss! Hisssss! Hisssss!