Figure 1. Picture showing the main components of an electroencephalogram (EEG): electrodes attached to a person's head and a display showing brainwaves. Image via Bright Brain Centre (http://www.brightbraincentre.co.uk).
Figure 2. A screenshot of twelve seconds of EEG showing twenty horizontal line graphs: nineteen black brainwaves and a red heart rate (EKG). Image via William O Tatum, 2013, Normal "suspicious" EEG. Neurology 80, Issue 1, Supplement 1, S4–S11.
The black arrows point to evenly-spaced peaks in the first half of the figure; and the red arrows point to choppy patterns in the second half of the figure. Counterintuitively, on EEG, abnormal brainwaves (seizure) can appear 'normal' / evenly spaced, whereas normal brainwaves are choppy and weird!
For more, see my paper (https://doi.org/10.1177/0961463X20908079, ask me for the pdf!)