Is man's brain really in his trousers?

I ALWAYS thought a man's best friend was his dog. Apparently not. It's a very different creature, more of a one-eye trouser snake.

The superior, the boss, the chairman... the documentary Man's Best Friend is never at a loss for words to describe the male organ. Neither are the men and women talking on camera about their experiences with "your best buddy - you are in there every situation together". As someone notes: "Dick seems to fascinate everyone", and they're not talking about Mr Turpin.

We follow the rise of the penis from coffee morning mothers comparing the size of their babies through the problems of puberty to "the social life of your private friend". For men, there's an insight into what women think of their genitalia, and for women, confirmation that a man's brain is in his trousers.

Various issues are discussed, including a claim that men are better than women at oral sex, and the intimate relationship between hand and gland. One man says he masturbates "for the sake of it, like opening a packet of crisps". No mention if they're cheese and onion or salt and vinegar.

Size clearly matters. An expert shows the correct way to measure the penis. The moment after he declares what constitutes a "normal length" sends men up and down the country scurrying to find a tape measure. If they feel they fall short, the marvellously-named Dr Long has invented an operation to make it, what else but, longer.

One woman is intrigued to know what life would be like with one, although the only advantage she mentions is the ability to go to the toilet more easily in the street when drunk.

I hope the men from Coupling take note of the findings as they are forever getting into scrapes through their sexual urges. The basis of this week's episode Unconditional Love took some swallowing. We had to believe that a man would turn down an offer of "no strings, no conditions, just sex" from the delicious Emilia Fox - or rather, the character she's playing.

Insane Welshman Jeff (the marvellous Richard Coyle) rejects her suggestion with the aid of his friends, who are in the pub listening in and advising him via his mobile phone.

The script, as usual, is a brilliant little mini- sex farce that demonstrates man's best friend can also be his own worst enemy.