mcdonalds-mouthoffFast-food giant McDonald’s has launched a new branded smartphone app: MouthOff McDonald’s. It’s available as a free download for Android and iPhone in the US.

The app invites fans to “have a little fun with one of our sound-reactive graphical fish mouths”, in what looks like a licensing deal with UK studio ustwo, which released the original MouthOff app.

In fact, this isn’t the first branded spin-off for the app, which displays cartoon mouths on-screen that move in time to spoken words – the idea being users hold their iPhone in front of their mouths for comical effect.

The original unbranded MouthOff app was released in March 2009, and has been one of the studio’s most popular apps. It has also spawned branded versions for children’s brands Ben 10 and Moshi Monsters. Overall, MouthOff has been downloaded by more than 5.8m people since the original version, according to ustwo.

“Be Frankie the Fish, a kissy-face puffer fish or whatever suits your taste,” suggests the App Store listing for the new McDonald’s version. “Simply choose a mouth and put your phone to your face. Now talk, shout or SING! Or, just hit the music button and get your Fishy-Fishy on with a serenade from your favorite mouth.”

Wondering what that looks like? Be our guest: