Dead skin. My fingers are coated with it, calluses like I've never had before. Tender, sore fingertips.
I've been playing guitar about thirty years. Before that, I played classical violin for a few years. I played bass in the high school jazz band for a year (the band teacher really hated me). I briefly dabbled on the dulcimer. A while back, I bought a 6 string banjo which is strung like a guitar (some people call this a banjitar; these people should suffer great pain and agony for their sins). So I have a varied background on many stringed instruments.
None of these has confounded me like does the mandolin. It's tuned way differently than the guitar, so not only does no knowledge translate, my knowledge of the guitar fretboard actually interferes with my mandolin attempts. The frets are very close together, so my fingers have to bend in new ways...so I don't even have muscle memory from which to pull. It has thin double strings under high tension, and these dig into my fingers.
I bought it over a year ago, but after playing it for a few weeks and a brief appearance on my album (just buy it already), I got busy and set it down. When I realized it had been months and months since I put it away, I vowed to make a concerted effort to become competent on the thing. For the last couple of weeks, I've been spending at least a couple of hours a day practicing. Today, I had stupid fingers that didn't want to cooperate with my brain (which itself had trouble switching into mando mode), but that's just part of it.
I don't expect to become bluegrass good on the thing...just competent enough to add different textures to my solo act and my next album. It's going slow, and it can be unbelievably frustrating, particularly with nights like tonight, where I was having trouble finishing a single song without stops and starts...but overall, I am (very) slowly getting better.
It's good, though, to challenge one's self, to push one's boundaries. Plus now, I can brag about my suddenly awesome calluses! Yeah....maybe that will make them ignore my whining about finger pain...