I’ve posted before about Shepard tones and other audio illusions, but here is another one to wrap your head around.
Jean-Claude Risset, who created the Shepard-Risset Glissando (a continuous version of the Shepard tones) also produced the rhythmical equivalent – a beat that appears to get faster and faster (and faster and faster). By layering beats with different related tempos (e.g. multiples like 30, 60, 120 bpm) the effect is of a never-ending increasing tempo – unless you shift your focus or pause and restart the audio.
Check out the original paper and the examples in the links above – does it get your heart pounding faster and faster!