The Cow Milking Contest has been a huge hit with rental companies for years. Kids love it because they get the chance to see what it's like to milk a real cow. Operators love it because they don't have the hassles and liability of letting kids milk a real cow. Educators love it because students learn through a hands-on experience where milk comes from. It uses white food dye mixed with water to create fake milk.
Easy to set-up, simple to store, and loads of fun to use. What's not to love about that?