This is a cool trick courtesy of Google: using the Google Search app on iOS or Android along with a special command leads to an unexpected response.
After launching Google Now on your Android device or Google's Search app on your iOS device, you simply launch a voice search (or you can type in the phrase) by saying, "OK, Google Now, let's go caroling."
In response, Google will provide you with a list of Christmas carols to choose from. Once you select one, you'll have the option to play the song, complete with lyrics and a bouncing ball to guide you through the precious holiday classics.
Sure, this isn't a ground-breaking feature or one that's going to have a long life after the holiday season comes to a close, but it's a fun one. It's a convenient way to spontaneously break into song, or entertain the kids when things are getting just a tad out of control.