The Tails of an animal are an important body part, due to its vulnerability. It is recommended for all animals, even the largest ones, to keep their tails well-guarded (this is relatively easy for King Dragons and Blue Whales due to their abilities), for the reasons below. Every animal except the Mouse, Shrimp, Chipmunk, Desert Rat, Rabbit, Trout, Arctic Hare, Desert Chipmunk, and Crab should watch their tails, these exceptions being due to said animals not having tails vulnerable to a tail-bite or being a Tier 1 animal which can't be bitten in the tail by anything. Crab doesn't even have a tail.
Tail-Biting is a game mechanic that allows a prey animal to fight back by biting the tail of a predator. If a tail is bite-able, it will be highlighted with a light green outline. The only animals without a bite-able tail are the Rabbit, Trout, Arctic Hare, Mouse, Shrimp, Chipmunk, Lemming, Snail, Desert Rat, Desert Chipmunk, and Crab. Animals that are neutral (with a dark green outline) cannot have their tails bitten, unless they are tier 15 or above.
When it occurs - although uncommon if a predator is at least somewhat aware of their surroundings - it counts as one bite and the prey gets 40 XP + 2% of the bitten animal's XP, said to be with a maximum of double the biter's current XP, even though there really is no maximum.
For example, assume a Rabbit that has 200 XP bites a Zebra that is less than 2K XP away from reaching Cheetah. When the rabbit bites it, the Zebra loses 400 XP (40+360(18000*0.02)), and the Rabbit immediately becomes a Fox, because it has 600 XP. The fox cannot bite tails for 3 seconds, due to upgrade invulnerability. If it were to bite 2 more times, then it would gain about 750 XP. Then, if it bites one more time, it immediately becomes a Zebra, about 1K away from Cheetah. A common strategy is for a small animal to wait until a predator is busy with other large creatures, then tail-bite it and run, gaining enormous amounts of XP for it's size.
- Some animals appear to have huge tails, but only a small part can be bitten. The longest tail is the Blue Whale’s, and one of the shortest tails is the Jellyfish's (with no visible tail at all).
- Before October 18, 2016, animals had absolutely no way of defending themselves against a predator, other than abilities and running away.
- After the update August 11, 2020, there was consequently a glitch created where tail biting gives no XP. This glitch is currently still in effect. It's sometimes due to the fact that when coming out of holes, there is a brief period of time where you are essentially in god mode except your ability will do no damage, and that you can't gain XP if you tail-bite during that brief period of time (formally you could lose XP by coming into contact with predators while in this "invincibility" which made the hole trick possible but now it's patched).