An open flap is an open invitation, and the visiting cat who accepts it rarely causes just one problem. Food disappears, trays get used by a stranger, and your own cat starts behaving as if her home is shared with an intruder she cannot remove. Understanding both halves, the feeding and the territory, shows why the fix has to control entry itself rather than chase the visitor out each time.
The Feeding Problems Come First and Look Simple
A visitor who eats your cat's food breaks measured feeding quietly. If your cat is on set portions for her weight or health, a neighbour's cat can consume a meal before she reaches it, while you see an empty bowl and assume she ate. The opposite error is just as common: you top the bowl up because she seems hungry, and now nobody knows what either cat has eaten. Food left down all day is what makes the visits worthwhile, so the feeding fix starts with set mealtimes, where meals are served, eaten and lifted, leaving nothing in the house worth entering for between meals.
Watch for the quieter signs too: your cat eating in a rush, eating only when you stand nearby, or guarding the bowl area. Those behaviours tell you the kitchen no longer feels like hers alone. If the visitor is also spraying near the flap or the food area, the feeding spot has become a contested boundary marker, and moving the bowls away from the flap end of the house can calm mealtimes even before the entry itself is fixed.
Territory Is the Deeper Injury
Cats read their home as territory that should smell of them and remain predictable. A strange cat walking in, sleeping on furniture, using the litter trays or spraying indoors overwrites that security in a single visit, and repeated visits compound it. The fallout often appears away from the flap: hiding in rooms the visitor never reaches, toileting away from trays that now carry a stranger's scent, over-grooming, appetite changes, or new tension between resident cats who previously lived peacefully, because stress in a shared home gets redirected at whoever is near.
Trays placed near the flap make the problem worse, since the resident cat must toilet beside the very door her rival uses, in the spot where she is least able to relax. Moving the trays beyond the flap's sightline, into quieter parts of the home, gives her a toilet area that feels defensible and private again. Extra trays during the unsettled period can help where space allows, and every soiled spot the visitor leaves should be cleaned thoroughly, because the scent alone invites a return visit.
Control Entry, Then Mend the Rest
Fit a flap that discriminates: a microchip model, or a magnetic version that unlocks only for your own cat. A chip flap works as a reader at the door: it reads the chip number of a cat pushing against it and unlocks only for the resident chips registered to the flap, which is a different thing from the chip registry itself, since the flap makes the entry decision and updates nothing. A magnetic version releases for the magnet on your cat's collar instead, and suits a cat who reliably wears one. Either way, test the flap with your own cat until she uses it confidently, because a resident cat frightened of her new door has simply swapped one problem for another.
Speak to the neighbour once entry is controlled, in friendly terms: most owners have no idea their cat is dining elsewhere, and knowing your cat's mealtimes helps them recognise when their own cat comes home suspiciously full. Keep the household consistent while the fix beds in, with everyone serving meals at the agreed times and nobody leaving food down for a cat who asked late. In KinsLe, Family Sharing shares one profile with the family members who help care for her, so the mealtimes, tray changes and the flap routine everyone follows are the same written version, not four remembered ones.