This is a fun thing to do with kids. Dave Hax shows you how to make magic goo that is solid if you roll it in your hands, but as soon as you stop, it will run through your fingers.
All you need for this science project is cornstarch or corn flour and some water. You can add food coloring if you like.
Note: Do not pour it down the drain. Pour the contents into a bag and throw it away in the trash.
Source: Dave Hax