If you purchase the tiger's tail while at 1 heart and 2 max hp, you end up with 1 empty heart and become unable to interact with coin pickups, heart pickups, and the sneaker relic (I left it in on the floor in the starting room). You are still able to interact with the boss room spellbook and the stairs, and can still die by getting hit. idk if you can still interact with the shop because I had 0 coins lol.
Edit: It also happens if you buy the tiger tail with 1 max HP.