I was getting a cup of coffee from my kitchen which looks out over the East of the town. I live on the top floor and have lived here for over 6 years and am well aware of what sorts of things I'm likely to see in the skies over town. There is a local hospital that gets visits from the air ambulance several times a week and also a local police helicopter that is bright red and instantly recognisable. A few miles away there is a training camp which used to be an airfield and rescue helicopters are still based there. I mention these because I am well aware of what a helicopter looks like and have seen aircraft of all types close up and from a distance. My eyesight is also excellent for my age (48).At 9.30am on the 8th of February 2008 as I stood waiting for the kettle to boil for a cup of coffee, I witnessed a strange object pass over town from the South on a Northerly heading. The object appeared to be only a few hundred feet above ground level and was almost at eye-level. It was a clear sunny morning & I was instantly confused by what I was looking at, as it didn't look like a bird or a helicopter or anything instantly recognisable, so I opened the window to listen, but heard nothing but the usual morning traffic in town.As I watched it seemed to shift its shape almost like a coiled up worm or snake tied in a knot, but it didn't get any bigger or anything. It was dark in colour, almost black/grey and when it moved like that I got the distinct feeling I was looking at a creature not a craft. As it got past town I noticed that there seemed to be something under it and I watched as it went over a hill.Once I couldn't see it anymore I went to the front of the property to see if it was in sight but it had gone. The entire incident had lasted no more than 30 or 40 seconds and I was left very puzzled as to what I'd just seen.On reflection about half an hour later I saw a helicopter pass at the same angle of view from my kitchen and it struck me that what I had seen earlier was either very big or had been much closer to me than I initially thought. If it had been an aircraft on the same heading, it would have been about 10 times as big as the RAF rescue helicopters. If it was closer then it was still bigger than a London bus and yet there was no obvious sound coming from it when I had opened the window. Nobody else I know saw it but it was all over very quickly in about 30-40 seconds and if I had been pouring my coffee I would have missed the entire episode.I could do a sketch if neccessary as I am an artist, but all I would draw would be a dark blob like a dark knot changing shape (like a writhing snake) with an odd hazy area underneath it.