Just Close Your Eyes
ת”ר, שבעה פרושין הן: פרוש שיכמי, פרוש נקפי, פרוש קיזאי, פרוש מדוכיא, פרוש מה חובתי ואעשנה, פרוש מאהבה, פרוש מיראה. פרוש שיכמי – זה העושה מעשה שכם. פרוש נקפי – זה המנקיף את רגליו. פרוש קיזאי – א”ר נחמן בר יצחק: זה המקיז דם לכתלים.
מקיז דם לכתלים – עושה עצמו כעוצם עיניו שלא יסתכל בנשים ומתוך כך מכה ראשו בכותל והדם יוצא.
Our Rabbis have taught: There are seven types of Pharisees: the shikmi Pharisee, the nikpi Pharisee, the kizai Pharisee, the ‘pestle’ Pharisee, the Pharisee [who constantly exclaims] ‘What is my duty that I may perform it?’, the Pharisee from love [of God] and the Pharisee from fear. The shikmi Pharisee-he is one who performs that action of Shechem. (see Gen. 34) The nikpi Pharisee-he is one who knocks his feet together. The kizai Pharisee-R. Nahman b. Isaac said: He is one who makes his blood flow against walls.
Rashi, s.v. meikiz dam le-kotalim (makes his blood flow against walls): He makes himself as if he closes his eyes in order not to look at women, and as a result of this he knocks his head into the wall and blood comes out.
The above text in its entirety is very interesting, and is found in a number of places with variations between them. See Avot de-Rabbi Natan, version B, 45 (Schechter ed., p. 124, here for English trans.), version A, 37 (p. 109); Y. Berachot 9:5, 14b; Y. Sota 5:5, 20c. This source has been discussed with relation to the identification of the Perushim and rabbinic asceticism. Regarding the former, see this important article by Shaye Cohen, and with regard to the latter, see this article by Steven Fraade. Also see this post at On the Main Line. This source even makes an appearance in an official document of the Vatican.