When 3 people eat bread together, they are obligated in zimun.

The rule that the meal has to be permitted food to obligate zimun, but forbidden food does not warrant zimun.

A non Jew, woman, or slave cannot be number 3 for the zimun.

A waiter who ate a cazayis can can be number 3 with two people he was serving.

The source that the number 3 brings people together to thank HaShem is גדלו לה אתי or כי שם ה אקרא.

Amen shouldn’t be louder than the bracha. The translator shouldn’t be louder than the speaker.

There is a dispute if 2 people are allowed to make a zimun if they want to. Even if they could, it is wrong for a 3rd person to leave before zimun bc he is taking away the obligatory zimun.

Women can make their own zimun if they would like.

A meal of women and slaves if considered meal of פריצות and no zimun should be recited.

When the 3rd person has left the room, a zimun can still be made if they call out to him and he answers. But for zimun of 10, he must be sitting with them.

When there are only two people and no zimun, it is actually preferable for them to bentsh seperately.

When 3 people eat together and one wants to make zimun and leave early, the other 2 should not feel compelled to interrupt their eating for him. But if 2 want zimun, one is compelled to interrupt his eating for their zimun.

There should be a zimun even where there is no great person to honor.

Usually, one shouldn’t answer amen to his own Brachos. But after בונה ברחמיו ירושלים one should say אמן and show that the biblical bensthing is over.