Ideally, a single tube forms between the electrodes.
In practice, multiple tubes can form between the electrodes.
Each tube will generate electrical potential so the voltage across the electrodes becomes a (confusing) mixture of multiple signals. This makes analysis difficult.
If the unwanted tube(s) are mechanically broken the voltage across the remaining (single) tube can be monitored and analysed.
To prevent exposure, better to keep the cover on the container and break the unwanted tube(s) with disposable rod.
The frequencies of most other signals (mains, radio, etc) are much higher than slime so the PhySense software can filter out background electrical noise from other sources.