פירוש על ברכות 47:5

TWO INDIVIDUALS SLEEPING IN A SINGLE BED. See Artscroll note 11. Tosfos here is referring to the Gemara on 25b that teaches that when one’s ervoh is exposed it is forbidden to recite the sh’ma. There are various degrees of exposure as will be discussed in the Gemara there. And if you ask: How can he possibly be permitted to recite sh’ma, but he sees his own ervoh.¹This word ערוה when used in this context generally means one’s naked genitals.
And we can answer: that he puts his head out of the blanket. And if you ask: but his heart sees the ervoh? And we can answer: that this Tano holds that when one’s heart exposed to the ervo it is permissible to recite sh’ma. The rule that one may not recite sh’ma when his heart is exposed to ervo is the subject of a dispute. This Tano may hold like the opinion that is lenient in this matter. Alternatively, he is separating between his ervoh and his heart by holding his garment opposite his heart.

M. : Nehemiah.

Throughout this discussion it must be remembered that in the Orient it was the general custom in the Summer to sleep quite naked; cf. Lane, p. 158. Even in the Winter people often slept naked because of lack of clothing. See p. 157 n. 1.