I've been to many Shiva visits, Jewish Funerals and many wakes and Christian Funerals (primarily Irish Wakes). I find myself going into "auto pilot" on the correct custom and bereavement protocol... my husband is Jewish, he seems to know protocol at Christian wakes too... but it took us both some adjusting. At one of my first Jewish funerals, I brought flowers, having no idea it's not a Jewish custom, in fact it's never observed, they don't believe in cutting something "alive" to honor someone dead. The tradition for flowers in a Christian funeral home was from years ago before it was standard to embalm a body and the flowers were to help disguise odor from a decaying body. Of course that is not the situation anymore, but the expensive and elaborate flower arrangements are expected. My husband is still not comfortable to go up to an open casket, the Jewish faith never has an open casket, and their casket is generally a simple pine box, no screws, nothing elaborate. If you've ever been to a house when they are sitting Shiva, you'll frequently notice the mirrors are covered, the primary reason is because prayer services take place there and one must ensure that no one faces a mirror during prayer. The other reason is to emphasize that a mourner avoids vanity during the Shiva, focusing on their loved one rather than themselves during this period.
I just came from a Shiva visit tonight, it's comforting to go to the home of the recently deceased and greet the family, I'm as comfortable doing it as going to a funeral home - different customs and protocol interest me, I'm forever learning and feel comfort when different religions bring people together vs. a wedge from threat or indifference.