Double feh
במדבר כג ,ג: יִפֶ ש ךֶל יַו
Baal HaTurim says that the letter Fei of this word is doubled. (Rashi translates “And he went alone.’) This means that instead of the reversed letter Vov hanging from the left end of the top stroke of the letter Fei, it is a second letter Fei inside the larger Fei. (This appears four times in a pair of tefillin according to the Kabbalists.) The doubling teaches us that we have a PiSHPuSH (double Fei), an extreme effort at finding an auspicious time to invoke a curse.