Lobsters and Oysters

My grandparents are very good at giving me illuminating advice. I`m not sure what it illuminates, exactly, but illuminates it does, nevertheless.

"I`m thinking of teaching in Korea next year," I told them on Skype last night. "When I`m done with Japan."
"Excellent," my grandad said, while my grandma stayed silent (I think she just wants me to come home, now). "The world is your lobster, after all."
"It`s oyster," my grandma pointed out.
"I like lobster."
"It doesn`t matter. It`s oyster. The world is your oyster."
"I know that but I prefer The World Is Your Lobster."
"But Oysters have pearls."
"Not all of them don`t."
"But some of them do."
"But most of them don`t."
"Yes, but lobsters have claws. All of them."
"But they`re much nicer anyway."
"I don`t think so."
"At least they walk around."
"The world doesn`t walk around, though, does it."
"No, I suppose not. But Oysters are very stationary and closed most of the time."
"You know," I said to interrupt this highly controversial debate, "pearls are actually created by oysters when a piece of sand irritates them, and they cover it in mucus so that it makes it less uncomfortable."
"Well, there you go," my grandad said. "The world is not an oyster. That means that the best thing you can get is a piece of sand that irritates you, and even then it`s not very often."
"Hmm," my grandma said. "If that`s the case, I should have very many pearls by now, living with you."
"Absolutely," my grandad replied good naturedly. "But it still means that the world is definitely a lobster."
"Oyster," my grandma said, and that was the final word because she`s my grandma and so it always is.

I`m torn between opinions. Mainly because I`d like to believe that the world is neither a lobster nor an oyster, as both are quite uninspiring creatures; unknown for their creative or amusing talents.

Unlike, I`m happy to say, both of my grandparents.