To explain. If you spend most nights hissing "Austin" outside the back door like I do, it does sound like you're trying to whistle through the gap between your two top central incisors. As the subconscious sibilant simulation is quite therapeutic, I can catch Austin out on occasion just by whistling and sucking teeth in an inappropriate manner!
Anyway, he rushes up and says "Wot?" and I say "Oh, nothing!" Then of course we both feel a bit stupid and spend some time hurrumphing and clearing throats and not catching each other's eye. It's a bit embarrassing to say the least!