Normal, Ordinary, Usual
A viking with a mouth towel is a totally normal thing. It's ordinary.
Vikings get a lot of nasty stuff on their mouths from their messy eating and pillaging, so it makes sense that they'd all have mouth towels. It's as ordinary and normal as it gets, at least amongst the vikings.
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It's normal for a viking to have a mouth towel, but your sloppy farmhand friend Joe(じょう) has a mouth towel too. That's a habit that's only normal for vikings, so why does he have one?
When you ask Joe about his Viking mouth towel, he just tells you, "It's normal for everyone to have mouth towels. Totally ordinary." Now that you think about it, he really is a messy dude, so he probably needs it.