Sharing the butter

Hi,

One the harchakah activities prohibited by the sages for a husband and wife when the wife is a niddah is that of eating from the same plate.

This prohibition does not preclude taking from the same serving plate, such as using the same butter dish. One does not eat directly from the butter dish, and one does not put any surplus butter back on the butter dish, from one's plate.

(Rav Moshe Feinstein, Igrot Moshe Yoreh Deah 1:92; see more there)

Have a great day,
Mordechai