When Archie McPhee made and marketed his 'Squirrel Coffee Mug,' no one actually assumed that the tiny coffee mug could be enjoyed by an actual squirrel.
McPhee proved everyone wrong by capturing an animated GIF of an actual squirrel on a deck holding the tiny coffee mug. I don't know exactly what he did to get the squirrel to enjoy a tiny coffee like that, but it makes for a great viral ad campaign. Maybe he put some ground up nuts in there, or maybe it was a hazelnut blend.
The tiny coffee mug is obviously meant to be enjoyed by espresso lovers, but it's probably not the greatest idea to feed a squirrel espresso. McPhee's page to purchase the tiny coffee mugs even says that he is "not responsible for damage caused by jittery squirrels."