Once again, we save parts by allowing a variable number of balls in the bottom tray. If we feed the red ball directly into the XOR gate, there are two possible situations:
- If the gear bits initially both pointed right, then they’ll point towards each other after the blue ball has gone through. In that case, the red ball will go straight to the interceptor anyway.
- If the gear bits initially both pointed left, they’ll both point right after the blue ball has gone through. Of course, we know that this situation doesn’t lead to the interceptor, but we’re basically back at case 1 now (just with a red ball in the machine instead of a blue one). So that first red ball will reach the bottom tray, but then the second one gets intercepted.
This way, we save a couple of parts by leading the red ball directly into the XOR gate instead of having to pass it in through a crossover afterwards.