Reference for Yoma 1:7
בִּקֵּשׁ לְהִתְנַמְנֵם, פִּרְחֵי כְהֻנָּה מַכִּין לְפָנָיו בְּאֶצְבַּע צְרֵדָה, וְאוֹמְרִים לוֹ, אִישִׁי כֹהֵן גָּדוֹל, עֲמֹד וְהָפֵג אַחַת עַל הָרִצְפָּה. וּמַעֲסִיקִין אוֹתוֹ עַד שֶׁיַּגִּיעַ זְמַן הַשְּׁחִיטָה:
If he started nodding, the pirchei kehunah (the young priests) would strike before him with the (etzba tzreidah) [("pirchei kehunah":) Youths, whose beards have just begun to sprout (lifroach) are called "pirchei." ("etzba tzreidah":) the finger near the thumb. "tzreidah" = "tzarata deda" ("this one's match), i.e., the match of the thumb, which adjoins it. They would join the thumb to the finger nearest it, and release it with a snap so that the high-priest not fall asleep], and they would say to him: "Our lord, high-priest, stand [on your feet] and remove (hafeg) it [your warmth] once on the [marble] floor," [the coolness of the feet dispelling drowsiness. "hafeg" = "remove," as in (Beitzah 14a): "mefigin ta'aman" ("their flavor is removed")], and they would keep him thus occupied until the time for the slaughtering (of the morning tamid).