How are the clocks in our heads generated? Time is an abstract concept on which today’s society is completely dependent; it provides structure in the chaos of everyday life. Humanity has a certain compulsion to carve the days into minute-size fragments and in order to do so we are constantly surrounded by clocks and other time-telling-devices. However, even if we get rid of the clock strapped to our wrists, we cannot escape the one in our heads. The human brain keeps time, from milliseconds to the long ticking of hours, days and years. When having fun our brain seems to make time fly, whereas boring situations seem to last forever. How is this biological clock generated? And does our inner clock really speed up when having fun and slow down in boring situations?