Having painted before, they realize that their habits are going probably going to get paint all over them. Being good friends without many other clothes, they figure they'll have a laugh and paint in the nude.

Out of the blue, there's a knock and voice at the door "blind man."

"Oh, he must be here for a blessing. Should we get our clothes?"

"Well, if he's blind, I'm sure he won't notice and thus won't be tempted by sin."

Conceding the point, the first nun opens the door.

"Nice tits! Now, where would you like the venetian blinds?"