Real Christmas trees are not harmful to cats in and of themselves, but there are some potential dangers to be aware of. Cats may be attracted to the scent of the tree and may want to climb it or play with the ornaments, which could cause the tree to fall over. Additionally, cats may be tempted to chew on the needles or ingest them, which can cause gastrointestinal upset and other health problems. Finally, some real trees may contain sap that can irritate a cat's skin or cause an allergic reaction. So, while real trees are generally safe for cats, it's important to keep a close eye on them and to make sure that