Curiosity did what to the cat now?

I felt smart today in Microbiology.
We were discussing isotonic/hypotonic/hypertonic solutions, and Herr Professor asked what would happen to a red blood cell if it was placed in distilled water. People say nothing. Then they said it would shrivel. In my head, first thing he said it, I said it would swell with water and probably explode. Got it right.

Then he asked what solution would be necessary to have a RBC be in an isotonic solution. People eventually say, "Um, one with salt?"
"How much?"
"...90%?"
He laughed. A nursing student piped up "...9%?"
"It will explode"
After a few more seconds, I speak up from the back, "0.9% Saline Solution"
"Ah. Good! Finally! What salt?"
"Any non-toxic, preferably sodium chloride"
"Why?"
"....It's cheap."
And I was right x3<3