These are the results of work done by another group trying to replicate the testatika. They've kindly allowed me to display their results so that I can show that the result of interaction with grids like this is AC. Their set up demonstrates it more clearly than my setup does.

Some of my own demonstrations of this output are here and here.

The Setup and Results

A diagram of the setup is below. The input is DC.

The reasons for the different peak-to-peak voltages below is because different gap sizes were used between the lamella and the tasters (ES1 and ES2 above).