With both switches open, both transistors are in cut-off (not conducting), the lamps are out, and resistor end of the switches are at +E voltage through the left lamp and R1, in series, and through the right lamp and R2 in series. If the right switch is the first one closed, the current supplied from +E, through the left lamp and R2 supplies base current to turn on T2. T2's collector-emitter voltage drops to about 0.2V and supplies a current path through the right lamp, lighting it. Because the base current for T1 would be provided through R1 from T2's collector, which is now only 0.2V, T1 cannot be turned on...it's locked out. E has to be disconnected to reset the game.
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