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Laughing Like a Piskey, or Devilish Laughter
Cornish Fairy Folktale

A K Hamilton Jenkin, discussing being 'Pisky–mazed,' mentions the elvish laughter that taunted 'pixie–mazed' or lost folks confused by the piskies:

It was not always, of course, that help was not always at hand, and many stories told of lonely travellers who had been led so far astray as to have sunk down exhausted on the bare ground. Others have only released themselves by following the old people's advise and turned their clothes inside–out, in order to break the spell. Again and again these victims of these fairy pranks have described how they have heard the elfish laughter of their invisible tormentors, the expression 'laughing like a piskey' still proverbial among the older inhabitants of the dutchy.

(Jenkin, Cornwall and Its People, page 280.)