Discovered advancing menacingly on CIPR HQ in St James's Square, the creature was expertly scooped up by Behrens using a hard-backed envelope and a glass.
'It was forest green, as big as your hand and flapping its tail,' she tells us.
The RSPCA duly arrived to proclaim that the little fella was in fact an Australian crayfish. It had probably fallen off the back of a catering truck.
'We were told that coming from foreign parts, he would eat indigenous crayfish, and would have to be humanely destroyed by lethal injection.' Shame, it would have made a nice centrepiece on the CIPR barbie.