Ever since the Forrest family pet unexpectedly entered the food chain in Fatal Attraction, and Frank the mercury-faced leporid walked into Donnie Darko’s waking dreams, rabbits have been officially nibbling around the edges of the horror genre. Right now, they’re at 46th place in the freakiness rankings, sandwiched between abandoned rocking chairs and wind-up music boxes (well below the likes of staring twins and evil clowns). But if there was a moment when the placid little critters first extended their range beyond merely cute, I like to think I was there, and wailing in raw, unfiltered, primal terror.

That reaction was probably wasn’t what Richard Adams had in mind when he wrote Watership Down in 1972, his homily to the timeless rhythms of rural England. I doubt Martin Rosen and John Hubley, directors of the 1978 film version, wanted to scare the bejesus out of their young audience either. But one small section – the apocalyptic vision that leads skittish rabbit seer Fiver to encourage his warren mates to abandon their burrows – was far too vivid. Fiver sniffs around, a whisper of terror in the air: a fencepost rears up like a gallows; a cigarette singes the lush green. Then he sees it: blood blotting a vast field, threatening to engulf them all. Skeletal tree outlines crack like veins through the insanguinated sods. Their branches twist and undulate with queasy malice.

Facebook Twitter Pinterest That’s more like it … Watership Down. Photograph: c.Everett Collection/Rex

The horror, the horror! I was a kindergarten Kurtz; the toddler who had seen too much. It was like reality was melting. I have dim memories of fleeing from a dark cavern of a Newcastle cinema, desperate for bright air and parental comfort. I hadn’t been that scared since a few months previously, when the Wicked Witch’s whiz-bang explosive entrances in an open-air pantomime of The Wizard of Oz had caused me to beg my dad to get me the fuck out of there. I hope having a child of Petit Prince-like sensitivity went some way to compensating for their wasted entertainment overheads during those years.

Strangely, neither of my parents remember the Watership Down walkout, but I’ve been convinced for quite a few years that it happened. Fiver’s vision happens less than 10 minutes into the film, and I recall nothing else of it. Just the weird Mesoamerican-style creation myth that is the prologue, perfectly synchronised with my own primitive brainwaves to lull me into the story as it delivered its kick. I’m guessing I was about three when I watched it, so it was probably one of the first times I had seen a film on the big screen, if not the very first.

I can’t claim that watching Watership Down was some kind of formative trauma, and watching the offending extracts on YouTube (many now spliced to Clint Mansell’s Requiem for a Dream theme) has definitely put any residual demons to bed. There have been plenty of other times when, as a grown adult, it’s felt more legitimate to brick it in the face of cinematic terrors: the mechanistic fight-flight prodding of most slasher films usually does the job; or the spiritual degradation of something more realistic like Snowtown; or the time I was watching Ring home alone when the power supply failed just as Sadako was crawling out of her cathode-ray abyss.

But the fact so little sticks about Watership Down other a vague reminiscence of an unstoppable flood of rabbit-geddon into my inner self – the field of blood that was my blood – makes me sure I must have seen it then, when the fontanelles were still hardening and reality was not fully formed. The perfect point to be most affected by the subtlest of all horror sensations: the child’s belief that whatever you see is real. Adults hold that feeling at bay with laws that mark off the boundaries between fiction and reality, most porous when it comes to filmed images; those demarcations are what allow us to lap up a Game of Thrones decapitation, but recoil when an Isis atrocity appears in our Twitter feed. On some level, is there a difference? It can be kind of fun to blur the categories, a frisson plenty of horror films have exploited with suggestions that – Blair Witch or Paranormal Activity-style – their secret footage might be real.

Facebook Twitter Pinterest Watership Down. Photograph: Allstar/Cinetext/Nepenthe Films

The child doesn’t make those distinctions, of course. And we’re children again when we watch, not so much suspending disbelief as resuming belief. Watch the right (or the wrong) things, and it will change you for ever. It was a vision of fear that first hooked me on the power of cinema, but then you don’t always have a rabbit’s foot around your neck.