Srilakshmi and Fluid Mechanics

When I had just finished my undergraduate education - if someone had asked me "what is a fluid?", I would have answered immediately. After my Master's, I could still have answered the question albeit with considerable doubt and skepticism. After my PhD, I admit, I cannot answer that question properly.
Apparently, Srilakshmi has an idea. The other day, we were at the table eating lunch and my wife whispered "We have only a small quantity of curd left. I have added some water and made buttermilk out of it. Please tell Srilakshmi that it is curd and not buttermilk".
The time for curd rice came and Srilakshmi asked us "I want curd". We pointed to the buttermilk and said "here it is". She looked at it with some suspicion , took a spoon and stirred it.
Then she said, "appa... see, this is not curd. I am able to stir it easily. It has got to be buttermilk."
I laughed!!