Refusing Funnel

2 funnels
2 identical, clean, dry plastic 1-liter bottles
clay or play-dough
pitcher of tap water
1) Place a funnel in each bottle. Use the clay to seal the funnel in one bottle.
2) Place both bottles on the table in front of you. Pour water into the unsealed bottle to demonstrate what a funnel is supposed to.
3) Pour water into the sealed funnel, filling it to the top. Explanation: When you pour water into the bottle that isn't sealed, the air inside it escapes through the opening at the top. But the in the sealed bottle, the air can't escape, that means the bottle has air pressure. The water has the force of gravity, but the air pressure inside the bottle is too strong, so the air can't get in, or can get in only in little drips.