After Series One, Howard and especially Vince undergo Flanderisation. Vince becomes far more obsessed with fame and partying and becomes a lot more shallow and cruel. At first it looks like standard flanderisation, but in "Strange Tale Of The Crack Fox", it was revealed the Crack Fox used to be a friendly fox until he moved to London and became an evil drug addict, because the London Lifestyle is incredibly corrupting. In Series One, Vince and Howard lived in London, but they spent most of their free time at the zoo and although Vince had a social life, neither were really involved in the London night life. When they moved into a flat in Series Two they were put right in the heart of London, and the London Lifestyle corrupted Vince (And Howard to a smaller degree) just like it did the Crack Fox.
In The Hitcher's third appearance, he appears to have lost his haggard skin and witch-like nose. At first, it may appear to be laziness or forgetfulness on the wardrobe department's behalf... then you remember that you last saw him being melted in the Fountain of Youth.
In "Eels", at the shaman stag weekend, why is Tony Harrison the most drunk out of all of them? He has the smallest body weight, meaning that his alcohol tolerance is lower than the rest of them.