Why do [cats' / cat's] eyes glow in the dark?

Kenny Chang

Senior Member
Hello, everyone.
I wanted to write a sentence like "cat's eyes glow in the dark," so I made up some possible sentences and used Google Books to check if the grammar was correct. And I found both of the following sentences:
1. Why do cats' eyes glow in the dark?
2. Why do cat's eyes glow in the dark?

I was wondering which one is correct? Because, biologically, cats' eyes are the same, this sentence can't refer to only one cat. Therefore, 1. makes more sense to me than 2.
Is 2. wrong?

Thank you for your help.
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