Walking towards the Strange Ox in the stables of the Last Light Inn will prompt a DC 10 Insight check whether you've seen it before; passing this check is not necessary to talk to the Strange Ox. With Speak with Animals, you continue the conversation you started in the Druid Grove. Regardless of what option you choose, you will need to pass a DC 14 Persuasion, Perception, or Nature check to continue.
Succeeding results in the Ox telepathically showing you images of disfigured corpses with the sound of screaming in the background. Failing the check causes the conversation to end, but you are still able to continue speaking with the Ox, essentially skipping the check.
Pushing it further results in the Ox threatening you. You can choose to either end it here, or continue questioning him. Questioning him further will result in the Ox turning hostile, deforming into a cyan version of an Ochre Jelly and entering combat with your party. Before doing so he tells the player he was only looking for a simple life of hay and a clean stable to live in. Killing the Ox here will cause it to drop the Hat of Fire Acuity. Alternatively, telling the creature that its secrets are safe with you will end the conversation peacefully ( +1 +1).
If the player character is The Dark Urge, they will relate to the ox's revelations and have the option to tell it about their own murderous nature, to which it will remark that the player may be a kindred spirit, but it only wishes to be an ox. The player can either respect it or chastise it for not giving in to its bloodlust - the latter option will cause the player to brutally attack the creature mid-dialogue, killing it without initiating combat as it struggles to retain its ox form until the very end.