Bring three or four people up the front. Show each participant (discreetly) the name of a well-known song.

One at a time, they then must take a mouthful of water then “gargle” the tune. The rest of the group needs to guess the song. It might be worth creating a list of suggested songs for the group. To make it competitive, you can divide the group (guys/girls or similar) and see who can guess the song the quickest.