I am left handed. When I was growing up, teachers tried to get me to switch. My mom let 'em have it.
That being said, I learned to do the sign of the cross with my right hand, left-to-right.
That ALSO being said, since I
am left handed, I have found myself making the sign of the cross with my left hand since to me it is natural to move my left hand first when I want to do something - pick up a pen to write, reach for my keys, use my computer mouse, and sometimes make the sign of the cross.
I know Byzantine Catholics make their cross right-to-left.
I don’t know what this particular priest has on his plate, but I know that several times the local Byzantine church has had a priest come from Latin rite to perform Divine Liturgy since they are currently without a priest. They have to get one that is “allowed” to perform an Eastern Rite (I don’t know how all of that works, that’s just what I heard.)
Anyway, if the priest is left handed he probably “instinctively” “reached with” his left hand to do the sign of the cross, and if he has had to perform some Eastern Rite services or what not (not sure of the correct word to use here) he may have gotten momentarily mixed up. And no, lefties do not do things in a “mirrored” fashion, we do things normally with the left hand.
Side note: I am dating a Byzantine Catholic man. When we sit across from each other and say grace before a meal, he does his right-to-left and I do my left-to-right cross. It’s kinda cool because our arms move together in the “same” direction.
Anyway… I wouldn’t freak out. I know that I have done this a few times being left handed. I had even made the cross with my left hand right-to-left rather than left-to-right. Now, I realize this is a
priest and we all know he “should know better,” but he is also human too and may have gotten mixed up.
If you MUST know, simply go up to him, “Hey! I didn’t know you were left handed! I know thus-and-so is. Not many lefties around!”
