My friend has a catflap and has often had marauders invading in the night
. Usually results in a big punch up, mass destruction and a pair of traumatised moggies!
Another side effect is the almost daily gathering up of body parts of their various victims. Not nice to step out of bed into mouse giblets
Our puss asks to go out as necessary and on winter nights is put out for half an hour at bedtime then returns to spend the night by the aga