What does it mean when...

you go outside and all the millions of birds that are chirping madly in the neighbors bush suddenly become completely silent.  From deafening chirp-itude to flat silence in a second.  It always makes me wonder if my hair is sticking up funny, or maybe I have toilet paper stuck to my shoe.  Whatever it is, those birds have noticed and they won't dare say a thing or they'll all die laughing.  Shakes my confidence, it does.