Heterodyning

Heterodyning is the combination of two or more frequencies to create new and different ones. It is also an extremely complex way of humming, which appears to aid a Spark in concentration and allow them to think more clearly.

The habit appears to be instinctive for members of the Heterodyne family, and in fact was the most obvious sign of Agatha Heterodyne's imminent breakthrough. However, it can also be reproduced mechanically, and might be imitable from memory.