The door of the red postbox clanks open, startling the swarm of occupants inside. The colony of bees springs into a flurry of activity, vibrating wings setting off a menacing buzz.
It is a warning for the intruders. But Mr Carl Baptista, 39, and Mr Elric Tan, 31, are not backing off. The bees don't know it, but they are being saved.
The duo are co-founders of Pollen Nation, Singapore's only conservation organisation that champions the bee cause.
"They are definitely pissed off," Mr Baptista remarks, pumping smoke over the nest to help calm the bees before conducting a "bee- vacuation".
The pair had been called to a house in the Holland Road area as bees had set up a hive in an ornamental postbox in the backyard.
Mr Tan, dressed in a white beekeeper suit, readies a modified vacuum cleaner with a plastic bottle attached to it.
With a flick of the switch, the bottle crinkles loudly, the vacuum pulling in several bees at once. In a few minutes, the bottle is full and it is swapped for an empty one.
This process is repeated until most of the bees have been removed and the honeycomb is visible. The honeycomb is cut away whole and packed.
When bees swarm or set up a hive with people nearby, a common response in Singapore would be to call in pest controllers who would spray insecticide on them, wiping out the entire colony.
Mr Baptista and Mr Tan know this all too well.
It was once part of their jobs.
Mr Baptista had been in the pest-control industry for over 15 years and he estimates that the number of hives he has eradicated is "in the hundreds".
Last year, however, he saw an opportunity to set up an organisation that would spread the bee-conservation message instead. He hopes to change people's perception about bees as pests, through workshops and talks at corporations and schools.
He says: "Many times, people kill bees because they are not aware or lack information. My job is to provide that information.
When people become informed, then they have a choice. It is up to them to make that choice for themselves."
To Mr Baptista and Mr Tan, saving bees is not about the honey, but the important role bees play in the environment.
Bee populations have been declining globally, affecting agriculture as bees have long been the world's main insect pollinators.
When bees go in search of pollen and nectar, their hairy bodies trap pollen and carry them from flower to flower, starting reproduction and the production of seeds.
Without pollination, many edible plants would not produce fruits.
The postbox bees have been relocated to Bollywood Veggies, a farm in Kranji, one of several adoption centres that welcome bees. Mr Baptista says: "I think the bees will be happy there."