Demo of multiplexing LEDs using an Arduino. The video starts with the multiplexing very slow, and gradually increases speed to reveal the words underneath.
The display has 10 x 74HC595 shift register chips. Nine of them are used to control the columns. There are 72 columns, so 9 x 8 (bits) = 72. The tenth one controls the 7 rows (the 8th bit is not used). Thus you can control 504 LEDs using only 10 chips.