Special dividends return a windfall without committing the company to a higher run rate. Because they are large relative to the price, exchanges apply different rules: a special dividend above roughly 25% of the share price moves the ex-date to the business day after the payment-date, and options contracts are adjusted rather than left alone.
That adjustment detail matters for anyone holding options through a large special. Strike prices are reduced, so a call does not simply lose the dividend.
Example: a $40 stock declares a $12 special dividend, 30% of the price. Options strikes are reduced by $12 and the stock trades with due bills until the delayed ex-date, so buyers up to the pay date still receive the cash.
Related: dividend, ex-dividend-date, payment-date, options-multiplier