1. An information processing system comprising: at least one memory operable to store program instructions; at least one processor operable to read said program instructions and operate according to said program instructions, said program instructions including: specifying instructions configured to cause at least one of said at least one processors to specify a content word co-occurring with onomatopoeia in one review among a plurality of posted reviews stored in a storage unit, each posted review containing one or more posted sentences; and extraction instructions configured to cause at least one of said at least one processors to extract a posted sentence containing the content word from the plurality of posted reviews.