meaning of ひょうたん ぽっくりこ in a song about a rolling caterpillar


I am reading a children's book written in hiragana. I saw the opening line of
the book mentioned online as being from the lyrics of a song, so I think this
may be a folk song or children's song.

The first line is: いもむし ごーろごろ

I translated this as The caterpillar started to roll (with the sound effect of
a large and heavy rolling object adding humor).

But then the next line confuses me completely. ひょうたん ぽっくりこ

My dictionary tells me that ひょうたん could be a contradiction or a gourd, but I
don't see how either of those ideas would fit in.




I'm a native Japanese, but I don't know the meaning of 「ぽっくりこ」.  
Visit the site <http://blog.livedoor.jp/season4/archives/9306591.html>, then
you'll know native Japanese don't know the meaning of 「ぽっくりこ」. So, you need
not worry about not knowing the meaning of 「ぽっくりこ」.

I'm not sure, but 「ぽっくりこ」 may be an onomatopoeia. When you tap at a gourd, it
will sound something like that.

At least, I know the 「ひょうたん」 in this phrase is a gourd, not contradiction. The
meaning of contradiction for 「ひょうたん」 is used only in the Japanese proverb
「瓢箪{ひょうたん}から駒{こま}」.  
瓢箪{ひょうたん}から駒{こま} could be literally translated like;  
A piece of shogi gets out of a gourd, upon which "shogi" is a game of Japan
like chess.

The proverb means;

  * What is not expected happens. 
  * An impossible thing happens. 
  * Something said as a joke actually happens. 

Similar proverbs in English are;

  * Many a true word is spoken in jest. 
  * There is many a true word spoken in jest.

[![enter image description
here](https://i.stack.imgur.com/fbAf8.jpg)](https://i.stack.imgur.com/fbAf8.jpg)




I'm a native Japanese, but I don't know the meaning of 「ぽっくりこ」.  
Visit the site <http://blog.livedoor.jp/season4/archives/9306591.html>, then
you'll know native Japanese don't know the meaning of 「ぽっくりこ」. So, you need
not worry about not knowing the meaning of 「ぽっくりこ」.

I'm not sure, but 「ぽっくりこ」 may be an onomatopoeia. When you tap at a gourd, it
will sound something like that.

At least, I know the 「ひょうたん」 in this phrase is a gourd, not contradiction. The
meaning of contradiction for 「ひょうたん」 is used only in the Japanese proverb
「瓢箪{ひょうたん}から駒{こま}」.  
瓢箪{ひょうたん}から駒{こま} could be literally translated like;  
A piece of shogi gets out of a gourd, upon which "shogi" is a game of Japan
like chess.

The proverb means;

  * What is not expected happens. 
  * An impossible thing happens. 
  * Something said as a joke actually happens. 

Similar proverbs in English are;

  * Many a true word is spoken in jest. 
  * There is many a true word spoken in jest.

[![enter image description
here](https://i.stack.imgur.com/fbAf8.jpg)](https://i.stack.imgur.com/fbAf8.jpg)

