Pure Titans aren’t driven by hunger the way normal creatures are. They don’t even have a functional digestive system—anything they swallow just sits in their stomach until they eventually vomit it back up. Their energy comes from sunlight, so eating isn’t about survival. Instead, they’re running on a deep, almost subconscious instinct to consume humans specifically in the hope of stumbling across a Titan Shifter. If a Pure Titan eats a shifter (particularly their spinal fluid), it can revert to human form and inherit that power. Animals offer none of that, so there’s no instinctual pull toward them at all. This also lines up with how Titans perceive the world. In the Rod Reiss sequence, we see things from a Titan’s point of view: the landscape is dark and muted, but humans stand out as bright, glowing auras that draw them in like moths to a flame. Animals don’t produce that same signal, so they’re effectively invisible to the Titans’ drive. That’s why scenes like the one with the deer grazing right next to a Titan’s leg make sense within the story—the Titans simply have no reason to register or attack them.