500
As there are children approaching other cages looking at the monkeys the children aren’t as entertained looking at them as when they meander to Slys' cage they notice that he's not just sitting there, he's actually working.
Run on sentence, to be verbs and contractsion - aren’t = are not, he’s = he is, he’s = he is, Repetition - they, they, children, children, missing comma - between monkeys and the children