Before one of my classes a 2nd grade student (limited English) came up to me and showed me her finger.
On the inside of the finger there were some red marks that looked like marker ink, so I pointed out where the tissue was and told her to clean her finger.
She came back a few minutes later and showed me her finger again; the red marks hadn't gone away.
I took her to our classroom where the light was better, and I had a closer look at her finger.
Somehow she had managed to hurt the finger on the inside, on the skin facing her palm.
I said, "Kate, this is blood!"
She looked at me quizzically.
I searched my memory and said, in Korean, "피!"
She said, "Yes!"
After I took her to the front desk to get a bandage (it wasn't serious, but I wanted to cover up the small wound) I asked a Korean co-teacher about the pronunciation of the word, since I knew that "blood" and "rain" sound very similar, at least to non-native Korean speakers.
Here's what I verified:
"blood" = 피 = pee (or "p")
"rain" = 비 = bee (or "b")
The problem is that, in Korean, the "p" and the "b" sounds are very close, so, for example, Korea's second largest city, Busan, is sometimes spelled "Pusan".
My Korean boss told me, laughingly, to make sure not to get the two fluids mixed up.