What made him do that?

I got a pressure cooker for Christmas. I pressure cooked a roast last week, using my pressure cooker for the first time. At the top of the pressure cooker there is this little knob thing, called a peacock, on the lid that will raise and let out steam and a little whistle to keep the pressure regulated.

My kids didn't know what to make of this. Mostly they just stayed out of the kitchen. Josh though, had to ask me something and ventured into the kitchen. Suddenly the peacock whistled and Josh covered his ears for a split second and then covered his crotch and ran out of the room. (sorry if I offend anyone) I thought, how the heck did he know to protect himself and why? I couldn't stop cracking up. I'm laughing right now and it happened before New Years.