What is 'Pitch Drop' experiment, in which only one drop of pitch fell after 8 years?

'Pitch Drop' experiment is world's longest-running experiment and was started in 1927 by Thomas Parnell of Australia's University of Queensland. The experiment aims to illustrate that everyday materials can exhibit surprising properties. It is a demonstration in which pitch, a derivative of tar, drops so slowly from a funnel that it took eight years for its first drop to fall.