In Japan pigs don't say "Oink," they say "Buu!" It sounds like "boo" and then "u" which rhymes with to. The Hiragana says "Buu" on each foot.
I emailed my friend Mayumi and asked her about it and here's what she had to say:
Those letters are Hiragana. 『ぶ』 ( Bu ) and 『う』 ( U ). 『ぶう』 is the "sound" we would say
if we wanted to put a word explaining about pigs. Your other three toes have a pig on each, so, I guess they put the word.
I bought these toe socks in the Shibuya Ward of Tokyo and they've become a big hit with the girls. Every time I wear them they don't stop with the "This Little Piggy" nursery rhyme.
This little piggy went to the market,
This little piggy stayed home.
This little piggy had roast beef, This little piggy had none.
And this little piggy cried "Wee! Wee! Wee!" all the way home.
My friend Laurel teaches English to Japanese kids at a school nearby. She said they play this out once a week and the kids get excited yelling "Buta!" Buta is the Japanese word for pig, and that's how they ask her to do it. Instead of a piggy buying roast beef, in her version it buys pizza. At the end she'll chase them around during the "Wee! Wee! Wee!" part and they climb under the tables trying to hide from her!
3 months ago