"...what things do they provide us? For instance, a donkey looks like a horse, except only it is smaller than a horse."
As you can see, the bold part confuses me. As far as I know, except is used as conjunction with a clause, such as:
"I would like to bail him out, except I don’t have any money."
I don't know whether the bold part in the sentence I posted above is grammatically correct. Please help me!