An inn-sewer-ants-poly-sea is a corrupted form of insurance policy. They are thought by most Ankh-Morporkians to be a sort of bet on the odds. The only known salesman of inn-sewer-ants-polly-seas was Twoflower, who sold one to Broadman, the owner of the Broken Drum, who proceeded to burn the pub down to try and claim the insurance. This started the Great Fire of Ankh-Morpork.