Have you seen people doing 'the twist' in the shallow water at a surf beach? Well, it's probably not some strange surf-dance-cult in action; people are probably hunting for Pipis.
Pipis are filter-feeding bivalves, that tend to live in the surf zone on large beaches, and are reasonable bait for a range of ocean, and estuary species.
There are a few techniques for finding pipis:
The Twist Edit
Wander down to approximately half way between the constant-water zone, and the unwet sand, and start doing the twist. Pipis that have 'holed up' tend to sit at around 10cm deep in the sand, and the action of your feet moving will generally find them. You may have to move along the beach to locate them, but where you find one, there will usually be others close by.
The water trail Edit
Pipis that are in the process of filter-feeding, will often produce a small 'v trail' in the water as the wave recedes. Works well on beaches that do not have much in the way of rocks, or large shells (eg: Cronulla, near Kurnell).
The collapse Edit
Pipis tend to leave a small bubble of air around them when they dig down. When you walk over them, this pocket will collapse - imagine a mine shaft folding. If you have sensitive feet, you can feel this slight collapse under your feet as you're walking past. Stop, and dig under that footprint, and there should be a pippi.
Fraser Flats Edit
On fraser island, you can often find pipis by wandering along the 4wd tracks close to the water - as the sand is compressed around a pipi, it causes a bit of air to 'puff up'. You then get a small 'dome' in the sand near the track. Dig down into the dome, and you're likely to find a pipi hiding.