Just whistle, Lauren Bacall

'To have and have not' Howard Hawks film,

Humphrey Bogart, Lauren Bacall, Walter Brennan

'...You know you don't have to act with me, Steve. You don't have to say anything, and you don't have to do anything. Not a thing. Oh, maybe just whistle'

You know how to whistle, don't you, Steve? You just put your lips together and... blow.