What will be the visible behavior of this Python code controlling LEDs on GPIO pins 12, 16, and 20?

What will be the visible behavior of this Python code controlling LEDs on GPIO pins 12, 16, and 20?

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
led_pins = [12, 16, 20]
for pin in led_pins:
    GPIO.setup(pin, GPIO.OUT)
for pin in led_pins:
    GPIO.output(pin, GPIO.HIGH)
    time.sleep(0.4)
    GPIO.output(pin, GPIO.LOW)