The formation of a unilateral contract can be demonstrated in the English case "Carlill v Carbolic Smoke Ball Co". In order to guarantee the effectiveness of the Smoke Ball remedy, the company offered a reward of 100 pounds to anyone who used the remedy and contracted the flu. Once aware of the offer, Carlill accepted the offer when she purchased the Smoke Ball remedy and completed the prescribed course. Upon contracting the flu, she became eligible for the reward. Therefore, the company's offer to pay 100 pounds "in return for" the use of the Smoke Ball remedy and guarantee not to contract the flu was performed by Carlill.