blinker circuit theory
The 100 ohm resistor driving the base of Q2 is not really low enough to drive it deep into saturation with a 3 ohm load, nor is the 120K resistor low enough to drive Q1 deep into saturation with a 100 ohm load, so there is positive feedback from the collector of Q2 to the base of Q1. 

As the voltage rises on Q2's collector (because the base current is dropping as the capacitor discharges through R2) it causes the base current of Q1 to drop and thus the base current of Q2, and at some point Q2 snaps off driving Q1 off and allowing the capacitor to charge through R4. 

If the load resistance is increased to (say) 300 ohms you'll probably see the circuit fail to operate.