For me, there are few things as revolting as snails and slugs (well, unless you include rats and pigeons). My disgust of snails and slugs was recently brought to a new level while watching a television show highlighting meningitis caused by a parasite commonly known as "rat lungworm." When an adult, this roundworm lays its eggs in the respiratory tract of a rat. The rat coughs up the larvae, swallowing and eventually excreting it. After a snail or slug eats the excrement of the rat, the rat lungworm finds itself in its second host where the larvae mature into adults. Rats then eat the snails and slugs and the cycle repeats. Apparently in humans (don't worry, it's quite rare) the roundworms can cause meningitis after accidental digestion.
While I'm certainly in awe of these sorts of complex parasitical relationships (I mean, imagine what must of transpired for this sort of choreography to have evolved), I still find it very disgusting.
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