However competitive, no amateur runner feels bad about being unable to see Eamonn Martin sprint for the finish. But it must be a different matter when an orange ostrich or a window cleaner carrying his step-ladder passes you and disappears over the horizon (never mind two guys pushing a model of Thomas the Tank Engine).
I have a theory about those who undertake the 26-mile jog disguised as rhinos, gorillas, clowns or badgers. Most of the outlandish costumes, I am convinced, are worn by solicitors, doctors and bank managers (972 of the 25,500 starters were accountants, according to the pre-race information) trying to hide their faces from clients. How would you feel if you spotted your GP among those sweating, agonised faces? That it was time to find a more sensible physician, I suspect.
But what is it that makes otherwise sensible men and women put their bodies through torment that, if inflicted on someone else, would bring a charge of grievous bodily harm? Some claim it's worth the pain because of the benefit to charities (estimated at pounds 4 to pounds 5m). That doesn't really explain it, though. For 364 days a year, most competitors are probably as uncharitable as the rest of us, remembering an urgent appointment or finding a building society shop window compulsive viewing at the rattle of a charity tin.
Yet Stephen Davies, who finished 24,603rd, claims he did it for charity. He raised about pounds 2,500 for his local hospital and for cystic fibrosis research, despite coming home more than six hours behind the winner. His average speed was somewhere around the pace of a rush-hour commuter fighting through the ticket barrier at a London station - but then, he covered the whole course on crutches.
A 32-year-old car mechanic from Dyfed, Davies lost a leg in a shotgun accident. Determined not to let the disability spoil his life, he took up hobbling. He has taken part in several half-marathons, but this was his first marathon. 'After 13 miles, I felt I couldn't do anymore. But I stopped for 40 minutes and got going again. It was very tough between 16 and 20 miles but from then on, everyone was encouraging me.'
It's easy to understand Davies's motivation. But why should a chirpy 23-year-old woman, with nothing to prove, give herself such suffering voluntarily? Tina Dorrell, from East Croydon, was walking on crutches herself this week after staggering on to Westminster Bridge just inside nine hours, an average of a mile every 20 minutes. Though she was last, five minutes behind even Davies, it was amazing she crossed the line at all. The farthest she had ever run before was three miles. She, too, claims her motive was to help the British Lung Foundation after discovering that her mother had lung damage.
'I started running three times a week but in February I pulled my knee ligaments. I didn't tell anyone. I had too many sponsors by then.'
Imagine setting off on a race nine times farther than you have ever run. Dorrell, who works in an opticians, says the first five miles were fine. 'Then it got harder. My legs and knee started to go. Around 10 miles was the worst. It was like treading on hot coals. The St John Ambulance people got out the silver blanket and said I should quit. But I was determined to finish. Next year? I would prefer to do a bungee-jump: it is over quicker.'
Dorrell, brave as a Benetton ad but hopelessly unprepared, got into the marathon simply because there are no entry qualifications. Most of the 70,000 who applied were far more suitable, but the race, now sponsored by NutraSweet, is for anyone fit or foolish enough.
Allan Haines, editor of Today's Runner, a magazine for fun runners (surely a contradiction in terms) believes the organisers should impose quite stringent entry conditions.
'I don't want to be elitist but people should be aware what the London Marathon involves and treat it with respect. It is not a game. It's very demanding and if you're not trained, it is hell. Everyone has a right to take part, but you should be doing at least six months training, and running at least 60 miles a week. Walking after five miles is not really taking part in a marathon.'