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Cats love looking out through windows, a pastime often known as cat television. It's a form of entertainment that is often instinctual. Glass window inserts that have the cat flap can be fitted to existing doors or windows. They can be put in double-glazed. Easy to install You can get cat flaps fitted to all types of doors and windows made of glass including double glazing, single glazing, french doors and patio doors, bifold doors and leaded units. They are great for people who do not wish to cut into their walls or doors