My boss is singing

Well, humming actually. He's right behind me, probably craning forward to see what I'm typing. I couldn't believe my ears. Hilarious. Refreshing. Amid all sorts of pressures, a guy still hum along to some tune. [Couldn't quite make it out. Probably zilizopendwa. Which reminds me. My dad also used to hum sometimes but I always swore that there were no such songs. Tu tuuu turuuu...]