Ruth 3:7

‘ And when Boaz had eaten and drunk, and his heart was merry, he went to lie down at the end of the heap of grain, and she came softly, and uncovered his feet, and laid herself down.'

There would be a good number of people present for the threshing, and all these would join in the feasting, and then seek out a place to sleep on the threshingfloor, probably a little merry from the wine. Boaz in his turn, once he had eaten and drunk also sought out a place to sleep, and he chose to lie down at the end of the heap of grain. Observing this, Ruth gave him time to settle and fall asleep, and then approached him softly, uncovered his feet, and laid herself down under that portion of his robe. It should be noted that she would remain fully clothed.