Until recently, the kid's been pretty uninterested in mimicking us. She'd do a sound now and then, but she's been more an independent observer who'll do her own thing for her own reason, not just because we're doing it.
Then last night after dinner, as my wife and I were whistling an assortment of the most annoying ringtones possible, the kid, thoroughly amused, started trying to whistle. She didn't put her lips together and blow, she put her lips together and made little high-pitched, sing-song hums. She was very pleased with herself.