One I saw in NZ had a stiff spring on the bottom and a miniature boot on the end (possibly a kiddy's).
The beater was an axe handle so it had shape to allow you to hold it loosely and still hang on to it. But the real wheeze was that it was serrated along one edge. Quite large lumps, which could be rubbed against the stem to produce a quick rattle, or banged against the stem.

Very effective it was too.