>>50826326I mean in general, it's just an inoffensive habit I noticed.
As for the poison, I don't know about the anime/manga but the only poison move it can learn appears to be Toxic. Then there's this from the wiki:
>Umbreon's Pokédex entries from Pokémon Gold, Stadium 2, LeafGreen, HeartGold, Sun and Sword refer to "poisonous sweat", which might be a holdover from the Pokémon Gold and Silver Spaceworld '97 demo, where Burakkī (later romanized as Blacky) is a Poison-type Pokémon. 