식해먹은 고양이 속, 식혜먹은 고양이 속,

'Cat's stomach after eating 식혜(shikhye)'
This proverb means “the feeling of worrying about committing a sin and being exposed for it.”

"삭해 먹은 고양이 속 shikhye muk eun GoYangE Souk"   

"식혜 먹은 고양이 속" and  

"식해 먹은 고양이 속" were mixed together 

and then"속 Souk" was missing.

So now 

"식혜 먹은 고양이" and 

"식해 먹은 고양이" are being used interchangeably.

The meaning of this proverb or phrase is a metaphorical expression of the fear of one's sins being revealed.

However,

식혜 Sikhye (食醯) is a traditional Korean drink made from rice,

and 

식해 Sikhae (食醢) is a traditional food made from fish, salt, and rice.

In other words, the cat ate not a drink but a stolen fish.

The 醯 Chinese characters are the same, and the pronunciation is almost similar.

That is, to use it correctly,

it should be "식해 먹은 고양이 <--- eating a fish" and 

not  "식혜 먹은 고양이"

However, although 식해 and 식혜 are used separately, it is not easy to distinguish them in everyday life. Even, 식해 and 식혜 are used interchangeably in everyday life. 

That is why "식혜 먹은 고양이" is used more often.

So, many people wonder, did the cat drink the water from the 식혜? Did it eat the rice grains inside the 식혜?

But the truth is, the cat stole 식해's fish.

**TIP**

Fish come from the sea. Just as the sea is called the ocean(해 海), if you memorize it by connecting it with the식해, it will be remembered unforgettably.