What is FACS?
The Facial Action Coding System was developed by psychologists Paul Ekman and Wallace Friesen in 1978. It describes every possible facial movement through a set of "Action Units" (AU).
The 17 Action Units in Red Rabbit
| AU | Name | What it signals |
|---|---|---|
| AU1 | Inner brow raiser | Fear, surprise |
| AU2 | Outer brow raiser | Astonishment |
| AU4 | Brow lowerer | Anger, concentration |
| AU5 | Eye widening | Fear |
| AU6 | Cheek raiser (Duchenne) | Genuine joy |
| AU7 | Lid tightener | Tension |
| AU12 | Smile | Joy (or masking) |
| AU14 | Mouth asymmetry | Deception, sarcasm |
| AU15 | Lip corner depressor | Sadness |
Deception markers
When a person lies, FACS reveals characteristic patterns:
- . **Micro-expressions** — the genuine emotion leaks through for 40-200 ms
- . **Asymmetry** — one side of the face moves more than the other
- . **Delay** — a fake emotion appears with a delay of >300 ms
- . **Missing Duchenne marker** — a smile without AU6 = fake