The landlord is not limited to what they notice during the walk through. Some defects can't be seen without a thorough inspection. Pet odor may not be noticeable when the windows are open, but show up when they're closed and the air conditioning unit on. However, landlord has to send your refund/statement of deductions within a specified period of time of your move-out or the landlord can't retain any of the deposit. Each state has different set of rules as to the time period the landlord can hold the deposit and the procedure for inspection, return of the deposit, etc.