Holes in headgear
In both real-world and fictional depictions, animal or anthropomorphic persons may often wear headgear which may allow for holes through which outstanding body parts (i.e. horns or ears) may protrude. Oftentimes, just as with tailholes in the posterior area of pants, holes may be partial in size and allow for the body part to be slid into placed before an attached latch can secure the body part into the hole (by means of buttons, velcro, etc.).
In real-world depictions
In Japan, a common humorous wearing of urban-dwelling girls' clothing may feature features cat ears which protrude from the top of a cap, evoking catgirl characters.