Scientist using an electrical penetration graph (EPG) in a plant defence study. EPGs involve running an electric current through a plant and attaching it to a computer. A small metal wire is then attached to an insect or other small herbivore which preys on the plant, in this case an aphid. Whenever the aphid bites into the plant it completes the electrical circuit, and the computer registers an electrical signal. This data can be used to monitor interactions between insects and plants. This example was part of a study into the way plants defend themselves from herbivores at the Swiss Federal Institute of Technology Lausanne, Switzerland.