The one thing you must never admit when you are a film critic is that a film has turned you on.
Fear, excitement, anger, sadness, joy: All of these emotions are OK.
They are parts of the esthetic experience worth describing, analyzing and celebrating at length. But anything racier is a definite no-no.
So: When you're sexually stirred up by Marilyn Monroe in that silvery breath of a dress in Some Like It Hot, or Scarlett Johansson luring an unsuspecting Celtic supporter into a vat of alien acid in Under the Skin - which are all, of course, entirely normal, healthy things for a straight man in his 30s to find sexy - it is mostly considered poor form to let other people know.
Too often, though, this tendency toward discretion goes zooming off in the other direction - witness the stampede by some writers last year to declare, with a weary and supercilious air, just how unsexy they found the Cannes Palme d'Or winner Blue is the Warmest Colour (an intensely and joyfully sexual film).
There's the whiff of a suggestion in such comments that having been turned on by a film is somehow a sign of weakness.
That attitude is dishonest, and doesn't reflect particularly well on any critic who perpetuates it without just cause.
This I am keen to clarify very carefully before writing that I found the newly released trailer for Fifty Shades of Grey as arousing as week-old meat loaf.
This two-minute clip gives us our first teasing glimpse of Sam Taylor-Johnson's forthcoming film adaptation of the incredibly popular novel, in which Anastasia Steele, a student journalist played by Dakota Johnson, strikes up an unconventional relationship with Christian Grey (Jamie Dornan), a wildly successful young entrepreneur with a serious penchant for sado-masochism.
The movie includes shooting locations in and around Vancouver. It will arrive in theatres on Valentine's Day, 2015.
Anastasia is the vulnerable ingenue, which we know because she has bangs and wears a blouse three sizes too big.
Meanwhile, Christian stands around beside ceiling-height windows and drapes himself broodingly across a grand piano.
He removes his shirt a few times, and there is a glimpse of ropes and whips.
The clothes, the decor, the shiny piano, the helicopter, the glider: Is it just me, or does it all look a bit like the "win Simon Cowell's lifestyle" clips they run as competitions on The X Factor?
If this gets you going (and the million-strong sales of the E.L. James books suggest it must be doing something for someone) then far be it from me to judge, although having now watched the thing five times over, I'm still not entirely sure which the sexy bits are supposed to be.
Even so, I'm prepared for the finished film to whoosh me off to untold new sexual zeniths.
And if it does, I'll gladly, if discreetly, admit to being whooshed.