During Nick and Ned's limerick competition, Nick uses the word 'Khaki'. This word is from the Hindustani language and only entered in the English language in the 1840s, through the British Army in India. As 'Swashbuckler' is set in the 1700s, he could not have known the word. They could be saying the word "cocky", which is more probable because its first printed use was in the 1700s and its oral use was even earlier.
When Jane Barnet challenges Ned Lynch to a sword duel on the beach, the shadow of the boom mic is plainly visible on the sand in the lower left corner of the camera view.