What are the three slots in a PAO image?

A Person (who), an Action (what they're doing), and an Object (the thing they act on).

Each item owns all three, e.g. one card might be Person: Einstein, Action: juggling, Object: a violin. In a composite, each slot can come from a different item:

• Person — a distinct, vivid character (celebrity, character, someone you know).
• Action — a clear verb, ideally that person's signature move.
• Object — a concrete thing they interact with.

Fixed roles in a fixed order are what let you decode the scene back later.

Go deeper:

• Mnemonic peg system (Wikipedia) — the standard person/action/object triad with worked examples.