This could work for any hollow figurine you have collecting dust on your shelves, but due to Android's open-source nature, a little robot is the obvious choice for DIY hackery. The full tutorial is on Instructables, but to make him react to sound; turn his head and flash his LED eyes in morse code patterns, you won't need many components.
In fact, here's the full list, if you'd like to get started on your shopping:
1 x Android Figure from DYZPLASTIC 1 x ATtiny44A from Mouser or Digikey 1 x 14 pin DIL socket 1 x Micro Servo SG90 (plastic) or MG90S (metal) 1 x Microphone e.g. CMC-5042PF-AC from Digikey 1 x Piezo (passive, not the buzzer kind) 2 x blue 5mm flat top wide angle LED from ebay 1 x red super bright 5mm LED 1 x green super bright 5mm LED 1 x yellow super bright 5mm LED 1 x NPN Transistor e.g. 2N3904 3 x 100nF ceramic capacitor 2 x 100K resistor 2 x 10K resistor 2 x 2K2 resistor (or other values depending on your blue LEDs) 3 x 150 resistor 1 x +5V power supply (e.g. USB charger)