The letter Peh is also the word Peh which means mouth. One of the hardest things to control is what comes out of our mouths. The tendency to engage in gossip (Leshon Hara, the evil tongue) is strong within human beings. By dominating the tongue, we elevate ourselves to the next level.
"The Holy One, blessed be He, said to the tongue: All members of the human body are standing, you are lying; all members of the human body are outside, you are guarded inside; not only that, but I surrounded you with two walls, one of bone and one of flesh; 'What shall be given unto thee, what shall be done more unto thee, thou deceitful tongue'!" -Arachin 15b"
"The talk about third persons kills three persons: him who tells the slander, him who accepts it, and him about whom it is told. -Arachin 15b"