I gather that this is about paying attention.
Incoming Bhikkhus' Duties
A certain incoming bhikkhu, unfastening the bolt and pushing open the door, rushed into an unoccupied dwelling. A snake fell on his shoulder from the lintel above. Frightened, he let out a yelp.
"An incoming bhikkhu, [C] thinking 'I will now enter the monastery,' having taken off his sandals, having put them down (close to the ground) and beaten off the dust, having lowered his sunshade, having uncovered his head, having put his robe on his torso/shoulder (khandha) (apparently, bhikkhus traveled with their robes over their heads), should enter the monastery properly & unhurriedly. As he is entering the monastery he should notice where the resident bhikkhus are gathered. Having gone where they are gathered -- at the assembly hall, a pavilion, or the root of a tree -- having placed his bowl to one side, having placed his robe to one side, having taken an appropriate seat, he should sit down. He should ask about the drinking water and washing water, 'Which is the drinking water? Which is the washing water?' If he wants drinking water, he should take drinking water and drink. If he wants washing water, he should take washing water and wash his feet. When washing his feet, he should pour water with one hand and wash it with the other. When pouring water with his hand, he should not wash with the same hand.
"Having asked for a sandal-wiping cloth, he should wipe his sandals. When wiping his sandals, he should wipe them first with a dry cloth, and then with a damp cloth. Having washed the sandal-wiping cloth, having wrung it out, he should spread it out to dry to one side....