I won't betray a confidence but I attended the press screening of a new movie recently that has a reputation for being something of a weepie. The nice woman from the film company came out to introduce it and said, jokingly, "I hope it will make you cry."

There's nothing worse than to feel as if you are being manipulated by a piece of fiction, and yet, when a film elicits an emotional response it is merely doing its job. What you are watching is not real - unless it's a documentary! - and is thus an illusion. 

If, for instance, George Clooney can make you cry when his character does in The Descendants, this is not an intellectual response, but a visceral, involuntary one. (He did, by the way, even though I knew with every fibre of my body that I was watching George Clooney acting, and pretending to be grief-stricken.)

I did not cry at the film at the press screening, as it happens, partly because I could see the emotional triggers coming, and felt disobliged to succumb to them. At no point did I suspend my disbelief and forget I was watching a film. Thus, no waterworks.

Films have much less work to do with me as I get older. I don't mind admitting that I well up more now than I ever used to. Do you get more sentimental with age? Maybe. Either way, I find myself tearing up, right on cue, more often than not. 

I watched Marley & Me when it was on TV a couple of years ago and, even though I know that no labradors were harmed in the making of the film, I felt every emotion intended as Marley went through his various life stages. (I had not read the book, but knew it was the "life story" of a problem dog, so the final button-push was pretty much expected. Mind you, I had wet eyes when Marley started to sit under the tree, looking a bit sad.)

I'm twice as soppy when it comes to animals, I don't mind admitting that either. Though I was largely unmoved by War Horse, I sobbed when a certain animal fell down on the battlefield, clearly on his last legs. I will cry at human tragedy, or even human triumph, in a film, but stick a pet in there, and I'm yours for the taking. 

The Artist made me cry, and I won't say when, in case you haven't seen it (has anybody not yet seen it?), but the dog was on camera. I saw a clip of the lovely but mistreated donkey in Robert Bresson's black-and-white Balthazar on The Story of Film on More4 and I found something in my eye. It was just a clip. Nothing bad happened in it.

This may well have been what was lacking in the unnamed, unmoving film I saw at the screening: it was all humans. They showed Courage of Lassie on the MGM film channel this week, in which Lassie - or to use his real name, Pal - plays Bill, who is trained as a war dog (and yes, it was clearly an influence on War Horse). When he's impounded, and then released, and reunited with Elizabeth Taylor? Not a dry eye in the house.