It seems i'm not the only spy..

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http://www.youtube.com/watch?v=d87QCn_cafI

If you have just escaped after been seen by an enemy and identified as a Spy while disguised, quickly change disguise to something different. Having just seen, say, a Pyro run through their base and sap all their buildings, the enemy will be on guard for any Pyros that they see for a while after. Changing disguise often not only helps in the short-term, but it will prevent the enemy from subconsciously associating your chosen disguise with ‘enemy Spy’ over the course of the game.