My experience leads me to suggest that the first possible explanation would be business meals, which are only deducted at 50%.
Other possibilities are items that you may routinely post to your books of account as expenses, which find their way elsewhere on the tax return, such as purchases to inventory or assets that are being depreciated over a number of years.
Any of these items would "shrink" your book expenses and result in a higher than expected net income.
For more information, please refer to:
IRS Pub. 535 Business Expenses
