Listening to this audio file you will hear the left and right hands beat together at 4 beats/measure for one measure.
Then at the start of the 2nd measure the right hand accelerates its beat rate speeding up by 3/2 beats per measure in each measure. This acceleration goes on for two measures until the rate of the right hand is 7 beats/measure. It takes 11 beats of the right hand to reach this new rate.
After reaching the new rate, the right hand stops accelerating and the two hands beat steadily, the left hand at 4 beats/measure; the right hand at 7 beats/measure.