Never assume it's ok to join a group. To avoid unpleasantness, ASK.

Kendall is right, in spite of being from Maine. Maybe it's his British wife. Better yet, listen for a while, then ask.

Keep in mind, at festivals, sometimes what looks like a jam is a group practicing for a set they're to do - especially when it's a pickup group formed for that performance. They really don't want any help at that point.

Agree on shaky eggs. Also spoons. Also bones, unless the player really knows his stuff and it's the right kind of music. Actually, that applies to most percussion instruments.

Of course, washboard players who attempt to join a jam that isn't jug band stuff, or zydeco, may be killed without notice, let, or hindrance.

Peter.