That’s maybe a weird way to put it when I could just say Two of my friends have cats. But that’s not the strange thing I have in mind.
What’s strange about 0.1 cats is the fact that you can use plural marking -s in cats. When we talk about decimals, including 0.1, we use the plural noun following the decimal: 0.1 cats, not 0.1 cat. Now, why is that strange?
Well, ignore for a moment the strangeness of the decimally dismantled cat and think about your conceptualization of plural nouns. When do you think you use the plural marker -s (cat vs. cats)? Most people will tell you that the answer is as straight-forward as 1+1 = 1: we use plural -s when we talk about more than 1 cat.