eruvin 26

studying torah outside a sick room may help the patient
or it may provoke the Satan.

but salt & water cannot be used to combine domains, and so the two can remain separate.

(discussion about the size of a royal court involves a story of Isaiah setting up torah study outside of King Hezekiah's room when he was ill. but one rabbi comments that this torah study may provoke the Satan, so perhaps is not a good thing. later in the page the next mishna discusses making an eruv, combining domains by sharing food. this can be done with any food other than salt and water. the salt therefore becomes a barrier. like for slugs....)