Give one of your guests one of the following names for the desired effect.

If you click on a duck when it is flying or swimming, you will hear a brief quacking noise.

When someone lets go of their balloon and see it rising higher and higher into the sky click on it and it'll pop!

You can have more than one person with the same name by changing the capitalization of the name's letters.
Example: There can be four or more Chris Sawyers in your park if one is named Chris Sawyer and the others chris sawyer, CHRIS SAWYER, and cHrIs SaWyEr.

In some versions of the game you can buy signs and there is a hidden trick you can use with this.

Place one facing away from the entrance right infront of it.
then right click it and click the no entry sign on it and none of your guests can leave.

When a guest is about to walk into your park, pause the game. Make the price of the park exactly one dollar less than what the guest is carrying. They'll always come in, no matter what. If it's the exact amount they have, sometimes they don't come in.

If there is a long line for a ride and you want people to get into it quickly, pause your game. Open up the ride window, double click the red light to close it and then double click the green light to open it. The ride should have reset itself, and all guests that had been on it are now at the exit. You should still have a line waiting to ride the ride. Unpause the game, and repeat as needed. *note: this will not work if a ride has broken down!*

If your grass is really getting out of hand, just choose the land leveller. Click once on the plot of grass and the tall weed will disappear. It still won't be freshly cut, but guests won't complain about uncut grass. Plus, it's totally free compared to the handymen.

You raise a piece of land as high as it can go. Put a guest on top of the land,and quickly lower it. The guest should fall down slowly. If not, try again until the guest falls slowly. When the guest is about to hit the ground, then quickly raise the land. If the guest already hit the ground, then the glitch won't work. If done correctly, then the guest should fall through the ground. Make sure that you have memorized the guest's name, and keep his window up. Eventually, the window will dissapear, and his name won't appear in the guest's list. So, the guest mysteriously dies.

Pick a random guest up with the pincer tool and hit backspace. The guest should remain in the position that he was in when you picked him up with the pincers.

Guests can actually walk across non-built paths. Just keep the path to be built flashing in the position you want it at, and guests will be able to walk across it like a normal path. Be warned, that if you move the path while a guest is on it they will fall to the ground.