This tiny interactive birthday present is all about minimalism.
It's heart is an Arduino mini-pro, connected to a battery, two LEDs as birthday candles, and a speaker that also doubles as a microphone.
When the Arduino is powered on, the LED candles lit up and a birthday tune is played through the speaker. After the tune is over, the LEDs remain flickering, waiting for the user to interactively blow the candles. The "air-blow sensor" is the speaker, reverse-operated as a microphone.