A lot of people were having trouble with this, so I figure I'd show this, where you can see when to swing for best results. I did screw up twice - once in the middle, one right at the end - but it worked out.
Make sure to swing AS THEY DO. Attempting to anticipate their motions will end badly.
Note I was playing this in 4:3, so like with BIT.TRIP FLUX, the letterboxing makes it smaller than the screen. I didn't have the time to swap to 16:9.