Don't buy hearts, use them instant instead. Fixes #38

squirrelbattle/interfaces.py

@@ -68,7 +68,8 @@ class Map:
         """
         Unregister an entity from the map.
         """
-        self.entities.remove(entity)
+        if entity in self.entities:
+            self.entities.remove(entity)
 
     def find_entities(self, entity_class: type) -> list:
         return [entity for entity in self.entities