Yes, it was a cardboard tube. No it didn't have a slug trail on it and no it didn't used to be inside a roll of paper towels.
Drum roll please.....
It was the cardboard tube inside a roll of foil. However, the cardboard tube was in the kitchen drawer where I keep the foil, waxed paper, etc. The box (also empty) was found on the counter. I don't even want to try to understand why my husband put the empty cardboard tube back into the drawer and left the empty box on the counter. Wouldn't you at least put the tube back into the box before putting the whole (empty) thing back in the drawer for me to find when I went to pull out some aluminum foil?
Thanks for playing - it was fun to see your guesses :-)