One of the replies briefly mentions coffee cup vibrations. There's a fun Numberphile episode just about this topic. https://www.youtube.com/watch?v=MfzNJE4CK_s

One of the replies briefly mentions coffee cup vibrations. There's a fun Numberphile episode just about this topic. https://www.youtube.com/watch?v=MfzNJE4CK_s https://www.youtube.com/watch?v=MfzNJE4CK_s By far, it is my favorite trick for impressing dining company.