Ruth 3:4

“ And it shall be, when he lies down, that you shall mark the place where he shall lie, and you will go in, and uncover his feet, and lay yourself down, and he will tell you what you shall do.”

But once he laid himself down to sleep Ruth was to mark where he lay down (darkness would be approaching), and when the time was right she should go onto the threshingfloor, lift up his robe where it covered his feet (Boaz would be using his robe as a kind of bedcovering) and should then lay herself down there and put that portion of the robe over herself. This was seemingly a recognised act by which she would be claiming the right of levirate marriage. It certainly indicated that she was seeking his protection. Boaz would then tell her what she should do. It would be in his hands how he responded to her plea.