Animals like cattle and deer eat the plastic because they can taste the salt left over from the food inside. These animals are often lacking salt in their diets, as their diets are deficient in this mineral... hence the reason they also go to salt licks, and eat soil high in salt content. Sea animals like turtles eat the plastic because it look and feels like their natural food of jelly fish and seaweeds. Ocean birds eat it for several reasons... so far as I have read. Mostly because brightly coloured plastics reflect light and look the same as their prey of fish invertebrates. As birds have a poor sense of taste they can't tell the difference. Fish eat the plastic as it looks like prey, and corals eat it as its got a chemical in the plastic that is actually tasty for the coral.