Basil the Rat (a.k.a. Rats) - S2-E6
Continuity mistake: When Basil and Sybil are talking to the public health inspector in the kitchen (on his second visit), Basil breaks two bottles of wine. When he removes the second bottle, there are two bottles remaining on the rack, but when the camera cuts away and then back when he breaks it, there is only one bottle left on the rack.
Chosen answer: Indeed it is Polly. She has stuffings in her mouth to pretend she is swollen.
Mortug