A mandolin can do a remarkable amount of damage. I occasionally encounter one guy in sessions round here who is a fairly good fiddler but occasionally decides to spend a session playing mandolin. On which he makes a pathetic tinkly noise barely recognizable as music. He will sit in a corner and *almost* start a tune for minutes on end - it is impossible to tell whether this is just noodling or if he's seriously intending to play a specific melody. So everybody politely keeps quiet and tries to figure out what he's doing. Usually, as soon as one person gets it and joins in (this person is frequently me), he abruptly stops. The result is to sabotage any impetus the session had going.