Gluing a magnet to the back of a cockroach turned out to be a bigger challenge than expected: the cuticle is slick and moist, the magnet is heavy (so likes to slide off), and all my usual tools are metal and instantly snap to the magnet. In the end, the solution was to first superglue a piece of acetate to the roach, then score the magnet to make it less slick, and finally superglue the magnet to the acetate. Despite the heavy weight of the magnet, and having it somewhat improperly positioned a bit too far towards the posterior, it seems to record the tiny movements produced by cockroach heartbeats, here about 1.3 beats per second.