A Halloween pumpkin project with a motion sensor and a speaker: plays a sound such as an evil laugh, when someone steps in front of it.
Plug the speaker in to pin 11 and ground. Using a small amplifier is highly recommended: not only will the sound be louder and have better fidelity, but plugging a speaker directly into an Arduino can potentially harm the Arduino (though usually nothing bad happens).
Plug the positive LED lead for the left eye into pin 5, the right eye LED into pin 6.
Plug the rangefinder's trigger pin into Arduino pin 7, and the echo pin into pin 8.