How many subjects does the first clause in this sentence have?
Her arms and legs and her fingers looked as if they had been stretched.
There are 3 'actors' that are being expressed ("her arms", "her legs", and "her fingers"), but really they're all filling the same grammatical subject 'slot' in the clause.
Her arms and legs and her fingers looked as if they had been stretched.
If we want to change the 'subject' of this clause, we simply change what's in that slot:
Her limbs looked as if they had been stretched.
They looked as if they had been stretched.
The sugar candies from the street vendor looked as if they had been stretched.
The rubber bands and the balloons looked as if they had been stretched.
So think about the 'subject' of a clause being a slot. It might have 1 'actor' in it, or 100 actors, or be implied, or it might not even have any actors at all (read about 'empty subjects' in the Simple Sentences lesson!), but there's always 1 subject slot that has to be filled by something.
Snippet source: Mosquito Advertising: The Blade Brief by Kate Hunter