Allan, tie up a dry fly, all except trimming the hackle and thread at the head.... turn your vise around so you are looking at the back of the fly.
Now, trim the excess at the head. Note the difference in how the scissors reach into the materials. Pay particular interest to the position of the blades, which is now opposite to what it was previously.
It is a small but important thing in fly dressing - much more important in cutting sheet metal, where the 'handedness' of the snips make the offcut rise to the right with right hand snips and rise left with a left-handed pair.
You cannot cut a curve to the left with right-handers. There are also straight snips.

Not everyone has heard of this, I have had some very strange looks in motor spares shops.. assistants checking to see whether it is April 1
Polka dot paint is harder to find.

;?}

Hope that helps,
all the best
Roy