Tensift · Ten cards. Four groups. One hidden rule.
Animals
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This page contains the answer to a past puzzle. Today’s puzzle is separate.
Frog · Crocodile · Turtle · Eagle · Penguin · Parrot · Dog · Elephant · Dolphin · Tiger
Test identity, not where an animal lives
The dolphin and penguin are useful stress tests for a proposed rule. Grouping everything that swims together feels natural, but it mixes animals with different biological characteristics. Try a classification that remains useful when an animal changes its surroundings.
The intended everyday vertebrate groups give the frog a one-card row, crocodile and turtle a two-card row, and eagle, penguin and parrot a three-card row. The remaining four belong together. Check the entire partition rather than treating “the leftovers” as a separate rule.
What the surprising cards teach
A penguin belongs with the other birds despite not flying. A dolphin belongs with the other mammals despite living in water. These cards expose the difference between a visible behavior and the category the puzzle is using.
A useful solving habit is to name your rule aloud: “how it moves” and “what kind of animal it is” are different questions. When one card keeps resisting a grouping, reconsider the question before assuming the card is an exception.
The limits of this simplified classification
The answer uses familiar school-level group names. It is not a complete evolutionary tree: modern phylogenetic treatments place birds within the reptile lineage. Here, “reptiles” means the conventional non-avian group used in the exercise.
That qualification matters because a puzzle needs a clear convention as well as familiar examples. If you find an alternative that applies consistently to all ten animals and preserves 1 / 2 / 3 / 4, report the full grouping so it can be examined.
The grouping
Each group is a vertebrate class: 1 amphibian, 2 reptiles, 3 birds, and 4 mammals.
- 1 · Amphibians
Frog
- 2 · Reptiles
Crocodile · Turtle
- 3 · Birds
Eagle · Penguin · Parrot
- 4 · Mammals
Dog · Elephant · Dolphin · Tiger