@jpm @whitequark (I know I'm preaching to some of the choir here)
But the twisted gnd is so effective because without it you only built half the circuit. Without a carefully run ground the other half of your circuit is more likely producing radio signals (literally) than doing what you drew in your schematic.
The mistake is that we don't draw circuits on schematics. We draw half circuits and a gnd symbol. It's not magic. But signals don't travel in wires but in the field between conductors.