Ok, so the 'trick' is to stick a paper fish onto the back of as many adults as possible, then run away yelling, "Poisson d'Avril!" (April fish!). Go!
Joyeux poisson d'avril!!!!
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Links:
[1] http://www.addtoany.com/share_save?linkurl=http%3A%2F%2Fthehindsightfactor.com%2Fpoisson_davril&linkname=Poisson%20d%27avril%21%21%21