This is a regular verb. It follows the conjugation pattern of the verb falar.
This verb is mostly used in Brazilian Portuguese. It can mean to dwell on or obsess over something. In informal Brazilian usage, it can also mean to get a strange idea or become suspicious without reason. In Portugal, it is rare and usually literary.
Present Tense:
Ele vive cismando com essa ideia.
(He keeps fixating on that idea.)