Why does my bag of Epsom salts say "Sodium Soak"?

[pulykamell]

I have 4 lb bag of Up & Up (Target) brand Epsom salts. The front reads (preserving the formatting as best I can):

epsom salt
magnesium sulfate
USP (heptahydrate)

saline laxative for relief of
occasional constipation
soaking aid for minor
sprains and bruises
Sodium soak

[Emphasis in the original]

The ingredients are 100% magnesium sulfate.

Is the “sodium soak” part a mistake? Does it have some other meaning I’m not aware of? There’s no sodium I could find here, so unless it means something like “soaks up sodium,” I don’t understand why it has that on the label. It’s just been bugging me for the past few weeks.

[Tim_R.Mortiss]

My guess is that it is intended to be used the same way a sodium-chloride soak would be used. Sort of like how people sometimes still say “tin foil” when the foil is actually aluminum.