Nautical folklore is rich with traditions that sailors believe bring "good luck" and safe passage. One of the most enduring "lucky" charms is the presence of dolphins swimming alongside the hull, which is seen as a sign that the sea is friendly and the journey will be successful. Another ancient tradition is placing a silver coin under the mast (or stepped into the foundation of the boat) during construction; this is believed to pay the "ferryman" for safe passage in the event of a disaster. Cats—particularly polydactyl cats (those with extra toes)—were historically considered lucky because they were excellent at catching vermin and were believed to be able to predict weather changes. Throwing a pair of old shoes overboard was once thought to appease the sea gods, though modern environmental laws have curtailed this practice. It is also considered good luck to "step off the boat with your right foot" first. Interestingly, many of these "good luck" omens are actually practical: for example, the presence of seabirds like the albatross was lucky because it signaled that land was near, even though killing one was considered the ultimate "bad luck" curse, as popularized in literature.