A four-legged gadget with a very special purpose
Cup-mounted turtle pours a perfect black and tan
A perfect example of the latter is this Brütül Lagerhead Black & Tan Turtle, featured in Popular Mechanic's "Top 10 Wild Kitchen Gadgets You'll Use Only Once." The sentiment written at the top of the article provides the best definition of the type of gadgets that end up making it onto our wish lists, describing them as things that "straddle the line between humorous and ingenious."
The turtle sits atop your glass as you pour alcohol into it, ensuring that they mix perfectly. You simply pour the lighter brew, add the turtle, and finish your glass off with the denser beer. Popular Mechanics gives the Black Velvet (Guinness and Champagne), the Snakebite (Guinness and hard cider), and the Bumble Bee (Murphy's and Dundee Honey Lager) as example beverages. If you're like me and you tend to put your faith in the pros, you can follow Brütül's suggestion and use the turtle to make its namesake, even if it's only once every couple of years.