The shutters were down, but the pub chatter in the midst of a coronavirus quarantine gave the game away a -crowded Brazilian bar operating under the cover of a pet shop with no pets.
Municipal authorities in the city of Petropolis said they discovered the speakeasy last Friday after neighbours complained.
Inspectors found 16 patrons drinking beer, none of them wearing a mandatory mask or keeping to social distancing rules.
"The owner served customers behind a closed door. They came in through the adjacent pet shop," a city spokesperson said.
The mayor's office said the shop, which had pet food but no animals, lacked proper registration papers.
Under lockdown in Rio de Janeiro, bars are not allowed to open while pet shops are viewed as an essential service that can.
The shop was closed after the raid and the bar owner fined.
Petropolis, a city of 300,000 inhabitants that was built up in the 19th century to the north of Rio as the summer retreat of Brazil's royal family, has had 92 deaths from Covid-19.
Rio de Janeiro is the second worst hit state in Brazil, with almost 10,000 deaths.