Why do we want to watch them and weep?

It is an odd thing to do isn't it? Why do so many of us voluntarily seek out a weepie at the cinema and put ourselves through a good cry? (By "we", this mostly means women, although that's not always the case). Is it for the visceral experience? For catharsis? To bond with the hundred other people snivelling into their Kleenex around you? Whatever the reason, if you're the sort who likes to emerge blinking from the cinema through puffy eyes and with a blocked nose, then look no further. My Sister's Keeper, the latest release to have audiences dripping into their laps. Several elements required for a proper cry are there: disease and the spectre of death throughout (in a child, which always works best), family pitted against one another and a tragic love story, thrown in presumably to make absolutely sure you're ferreting through your bag for that dirty tissue.

Death is the filmmaker's biggest gun when it comes to tear-jerking. It is most effective when the victim is young, but can be used to dramatic effect at any age, especially if there has been a battle leading to the death. In Forrest Gump, Jenny dies having supposedly contracted Aids; ditto Philadelphia. In Terms of Endearment, Emma pegs it having bravely fought cancer; in Love Story, young Jenny dies from a mystery disease - classic weepies, the lot of them.

And then there's death that doesn't necessarily involve prolonged and heart-rending illness, but has an added dimension of some sort. Enter Titanic, perhaps the biggest, blockbusting weepie of them all. We sob at Jack's demise both because he is gone and because this means that poor, upper-class Rose cannot run away from Billy Zane and slum it with him after all. Another tale of star-crossed love and one of the biggest weepies in recent years was The Notebook, which reportedly left many celebrities so puffy-eyed after the 2004 premiere that they went straight home without attending the after-party. But unlike in Titanic, here young Noah and Allie end up with one another and stay the course, irrespective of Allie's bout of Alzheimers in later life. Honestly, it makes no sense at all. We cry if they're torn apart, we cry if they stick together.

Naturally, we also reserve the right to splutter and sob even when love sometimes conquers death, as in Truly, Madly, Deeply and Ghost, the latter helped ably by a soundtrack that included Unchained Melody from the Righteous Brothers. But most of these films will only have women tearing up. So what about men? There must be something that gets them going. Well, it seems that war films are the genre most likely to trigger male tears. Perhaps it is the element of noble sacrifice that men like to empathise with, perhaps it is that films with guns allow them to feel suitably macho even while sobbing into their popcorn. The Deer Hunter could be inserted here, as could Saving Private Ryan. Braveheart, too, at a push.

Finally, there's the genre that can unite all audiences - be they, young, old, male or female - into one helpless blubbering mass: the animal film. Most recently, Marley & Me reduced fully grown human beings to quivering wrecks despite one stone-hearted critic grumbling about the lack of acting skills shown by the dogs involved. Hollywood has long used a beloved pet to play on the emotions - and none of them had been to drama school either. Think of poor Old Yeller, think of the 1940s Lassie films and of the multiple versions of Black Beauty.

Bambi, however, is a tough one, because it's a cartoon. Is it slightly shaming, that an animated drawing of a deer can reduce one to tears? Who cares. Sometimes you just need a good weep. * Sophia Money-Coutts