To trigger the Liz House Interaction in Animal Hospital, you first have to complete her quest of photographing four different anomalies. Once you've completed all of this correctly, Liz will come back to thank you, as well as invite you over to her house to show you something. If you want to know what she has unraveled, then keep reading!
As new lore updates are added to Animal Hospital, that means you'll get to discover new interactions with familiar and unfamiliar NPCs, including Liz. If you want to make sure you unlock the secret Liz House interaction in Animal Hospital, then make sure to follow our guide carefully below.
How to Go to Liz's House in Animal Hospital
For starters, you have to complete the entirety of the original Liz questline. Here's how you can do so in order to ensure you get to go to her house afterwards!
How to Complete the Liz Quest

When Liz first shows up, she will ask you to take a photo of a hospital patient for her. She will give you a name and leave if you accept. Don't worry if you don't remember the name. It's written on the wall on a post-it note. Too many people were finding it difficult to remember, thus the post-it note solution!
Important: You only have one chance to take a photo. If you capture the wrong patient, Liz will come back, be disappointed in you, take her camera, and leave.
Liz will ask you to take a photo of a patient four times in total. This patient is always a weird Anomaly, usually not noticeable on regular camera. You don't have to accept them as patients, all you have to do is get the photo before turning them away. Whenever Liz shows up with a new name, make sure to carefully read the nametags, or you risk skipping the person you need to photograph.
At the end of the quest, Liz will show up to thank you for your help with photographing the Anomalies as she managed to get it published. This may seem like a final interaction, but worry not. Liz will show up one more time.
How to See the Liz House Interaction
Now, keep in mind that you need to manage to reach at least 15 Shifts in order to actually get the Liz House Interaction. Realistically, it will happen some time around 17 Shifts, so the goal is to stay alive for as long as possible.

Hire Sam for help as soon as you can, as he can deal with Fires in various rooms as well as Slime and some Anomalies like the Hiders that can be extremely annoying. Another thing you should focus on is completing the Barney quest. Give him coffee whenever he asks, take his suitcase, give him a scalpel, and finally, let him hide in your office. Even though he has killer intent towards you, if you protect him, he will reward you with another Coffee pot. That means even more Sanity for you, especially since he won't be coming back to drink it from you.
When Liz shows up, she will thank you for your help as well as mention that she has something else to show you. You have to go to her house in order to see it. Just choose the first option, and after completing a shift, you will get a cutscene that takes you to Liz's House in Animal Hospital.

Here, she will show you around. There's a box of Pizza on the table, so make sure to pick up a slice. Pizza restores around 50 of your Sanity, so you definitely want to have it on hand. You can eat it in three slices, with each slice giving you more Sanity back, so time eating them for when you really need to restore it.
Related: Animal Hospital Classes Tier List
Liz will also show you a whiteboard with article clippings from newspapers talking about the hospital you work at, all of the strange anomalies, and how all patients keep coming back but looking worse and worse each time. Her photography quest was just the tip of the iceberg. She mentions that the Anomaly situation isn't an outbreak, since they happen spontaneously. This is scheduled, meaning something, or someone is doing the scheduling.
While at her apartment, she will get another visitor. Ratthew, who is very suspicious of anyone with a suitcase, shows up and talks about his little vent exploration at the hospital. He even recorded it, which you get to see by putting in the tape into the TV. You'll see sneak peeks into what future lore updates may hold.

However, this entire trip is cut short by another knock on the door, this time by someone who looks like the Secret Agent but in the Agent R skin. Liz will tell you to run away, and you will be teleported back to the Hospital to keep playing as if nothing happened.
One important detail from Liz's House is a map on the wall that seems to be of the Animal Hospital, with specific areas pointed out with question marks. We have no information on what these areas are just yet, but some sections could be behind the closed door to the left of the store.
How to Open the Closed Door in Animal Hospital

There is currently no known way to open the Closed Door next to Room 6 in Animal Hospital. With regular updates, the game also drops a lot of lore content, often locked behind specific quests in later shifts, think 10+.
Many speculate that the doors will be a part of a future lore update, coming on September 5th. While there is no way to open it right now, it certainly works to build the curiosity, as I'm personally very excited for the next update.
To get as many Animal Coins as possible, make sure to redeem all Animal Hospital codes!