Start the Havana Brown's introduction behind a closed door
A Havana Brown should meet a resident pet by smell long before she meets it by sight. Set her up in one quiet room with a litter box, water, food, a scratching post and a box or covered bed she can retreat into, and keep the resident pet out of that room entirely at first. Let her settle until she is eating, using the litter box and exploring the room on her own initiative rather than hiding all day.
Feed both animals on opposite sides of the closed door, bowls set a little back from it. A resident pet that eats calmly near the door is learning that the Havana Brown's scent arrives with good things, and the same lesson lands for the newcomer. If either animal hisses, stops eating or fixates on the door, move the bowls further apart and give that stage another day instead of pushing forward.
Swap scents before anyone sees anyone
Scent swapping gives a Havana Brown and a resident pet a shared smell before a shared room. Rub a soft cloth gently along the Havana Brown's cheeks, then leave that cloth near the resident pet's resting place, and do the reverse with a cloth carrying the resident's scent. Exchange bedding between the two spaces after a couple of days, watching whether each animal sniffs, rubs against or ignores the new item. Curiosity or indifference is the green light; flattened ears, growling or avoiding the bedding means the pair needs more time at this stage.
Brief room swaps come next, with no animal meeting the other. Put the resident pet in another room, let the Havana Brown explore the wider home and its smells, then return her before the resident comes back.
Move to sight, then short supervised meetings
A Havana Brown's first sight of a resident pet should happen through a barrier neither can push through. Use a tall pet gate, a securely stacked pair of gates, or a door opened a crack and held, and offer both animals food or play at a distance where each can look and then look away. If the resident pet is a dog, keep the dog on a lead, reward calm lying-down behaviour, and let the Havana Brown choose how close she comes; she must always have a high perch or an exit route the dog cannot follow.
Once barrier sessions look boring, allow a short meeting in the room with the most space and the most exits. Stay quiet, avoid picking either animal up, and separate them again at the first hard stare, chasing or cornering.
Keep separate resources until sharing is their idea
A Havana Brown sharing a home with a resident pet still needs her own resources after meetings begin. Keep separate litter boxes, feeding stations and resting spots in different areas so neither animal has to pass the other to eat, toilet or sleep. Resource pressure is behind many setbacks that look like sudden dislike: a cat blocked from the litter box by a resident pet standing in the hallway may start toileting elsewhere or ambushing from frustration.
If hissing matches, hiding or appetite loss persist beyond the early days, or any animal stops eating, go back one stage and hold there longer, and talk to a veterinarian if eating or litter habits do not recover. In KinsLe, Care Teams helps here by giving each introduction chore — door-side feeding, bedding swaps, supervised meeting duty — to a named person with a timestamp when it is done, so the Havana Brown never gets two stages rushed in one evening.