My parents adopted a quirky cat that seems to have had some past trauma. She's finally getting more friendly and less skiddish - AFTER FOUR YEARS.

Sometimes it's just love and time that helps them get over past trauma.

My cat was not a trauma victim, we got her quite young, but she sometimes still jumped out of her skin while doing nothing - because she got an itch. You'd see her skin twitch in a spot, and then she'd jump out of her skin to dash off to somewhere else just to scratch it. It was just the sudden unexpected unpleasant physical sensation that triggered her, so it's not always a trauma thing. Admittedly she was a rather flighty cat, despite her leisurely safe flea-free existence.

However, for a new rescue, they're definitely going to be extra jumpy for a while. I hate his format, but Jackson Galaxy gives solid and practical cat behaviour info. He doesn't go into trauma and memory anywhere near enough but here's a perspective on cat memory you might find useful. Maybe your cat remembers a smell from a cleaning chemical at the rescue place?

Give him nothing to be scared about and he will slowly forget.