Aggressive mimicry may be used by some parasites as a means of getting to their next host. A parasitic trematode (flatworm) lives in the gut of songbirds. Their eggs pass out, and are then eaten by a snail which lives in moist environments. The eggs develop into larvae inside this second host. Unlike related species, these larvae are brightly coloured and able to pulsate. A sac full of spores forces its way into the snail's eye stalks, and pulsates at high speed. This causes the tentacle to enlarge. It also affects the host's behaviour: the snail moves towards light, which it usually avoids. These factors make the sporocysts highly conspicuous, and they are soon eaten by a hungry songbird. The snail then regenerates its eye stalks, and carries on with its life cycle.