This morning something or someone tried to come through the cat flap.
Frillycat 1 (bossy) was there spitting and screeching at once and frillycat2 (nervous) provided backup from the doorway of the sitting room.
Frillycat 1 then attacked Frillycat2 and me - and ever since has been in a furious strop (huge fluffed up tail, glaring, hissing, jumps on Cat2 every time it tries to come out from behind the sofa).
Well Cat People - why is she attacking us? We weren't interfering with her flap!