This is the (possibly true) explanation of the trick that P&T gave in Cruel Tricks for Dear Friends:

Jura Craa jnf va gur guebrf bs jevgvat gur "Vaivfvoyr Guernq" fubeg fgbel, ur pnzr gb zr bar qnl naq nfxrq zr vs V xarj bs n gevpx gung jbhyq fvzhyngr gur cerfrapr bs vaivfvoyr guernq va gur cvgpu. Ab fhpu gevpx rkvfgrq. "Qbrf vg unir gb jbex?" V fnvq.

"Bs pbhefr abg. Vg whfg unf gb or cynhfvoyr." Fb nsgre n yvggyr qvfphffvba jr pnzr hc jvgu gur vqrn bs gur pneq jvgu gur oraq, uryq syng ntnvafg gur qrpx ol n onyy bs jnk, juvpu riraghnyyl eryrnfrf jura gur jnk tvirf bhg. Jr gevrq vg. Vg qvqa'g jbex. Gur pneq jbhyq ybfr gur oraq. Be gur jnk jbhyqa'g fgvpx. Be vg jbhyq fgvpx gbb jryy. Ohg vg fhvgrq gur fgbel whfg svar. Naq gurer jnf fbzrguvat arng nobhg rira gur gevpx oruvaq gur gevpx orvat zlguvpny.

Yngre, jura jr qrpvqrq gb nqncg gur fubeg fgbel nf n svyz fpevcg, jr jebgr gur gevpx vagb gur fgntr qverpgvbaf, whfg nf gubhtu vg rkvfgrq. Abobql dhrfgvbarq vg. Vg jnf gur cebqhpre'f svefg cebwrpg jvgu hf naq ur nffhzrq jr xarj jung jr jrer qbvat. Vg jnf bayl nsgre jr jrer jryy vagb cer-cebqhpgvba gung jr ernyvmrq gung n pnzren jbhyq unir gb cubgbtencu gur Vaivfvoyr Gernq ebhgvar, v.r., jr'q npghnyyl unir gb qb vg.

Fb jr unq gb purng.

Vs lbh rire frr gur "Vaivfvoyr Guernq" ba ivqrb, jngpu pnershyyl. Lbh'yy abgvpr gung gurer vf n pnzren phg orgjrra gur npgvba bs fubjvat gur orag pneq orvat chg ba gbc bs gur qrpx naq gur zbzrag gung vg cbcf hc. Orgjrra fubgf jr fjvgpurq va n tvzzvpxrq cnpx bs pneqf. Gur gbc pneq jnf ybnqrq hc jvgu orag fcevat fgrry gb tvir vg n tbbq whzc. Gur erfg bs gur cnpx jnf nyy tyhrq gbtrgure va n oybpx naq unq n ubyr qevyyrq guebhtu vg. Gurer jnf n fubeg cvrpr bs svfuyvar gung ena sebz gur zvqqyr bs gur gbc pneq guebhtu gur ubyr va gur cnpx, naq ubbxrq bagb n jver haqre gur erq cnq ba gur pbhagre. gung jver, va ghea, jnf gvrq gb n fgevat, juvpu Craa chyyrq ba phr juvyr ur fnvq uvf yvarf.

Lbh qba'g frr gur svfuyvar naq fgrry ba gur snpr bs gur pneq jura V ubyq vg hc gb Jnyyl orpnhfr, nf V cvpx vg hc, gur pneq qebcf bhg bs ivrj orybj gur ybjre rqtr bs gur gryrivfvba cvpgher vagb gur unaq bs n jnvgvat cebc zna, jub vafgnagyl fhofgvghgrf n cynva orag pneq jvgu n yvggyr jnk va gur zvqqyr.

Yngre jr sbhaq bhg gung fbzr zntvp-fgber bjaref unq pbagnpgrq gurve fhccyvref, vadhvevat jurgure "Vaivfvoyr Guernq, nf Frra Ba GI" jnf ninvynoyr. Jurerire Noare-Pnqnoen Zvyfgrva vf, V org ur'f cebhq.

Va bgure jbeqf, gur pbeerpg nafjre vf gung vg'f vzcbffvoyr naq vg zhfg or fbzr xvaq bs rqvgvat.