The Animal Sorter
Understand the puzzle
The exact puzzle
A zoo machine sorts animals by asking yes/no questions. Its first question is 'Does it live in the water?' — that sends the DOLPHIN and the FROG down the YES path together, and the EAGLE and the CAT down the NO path. The NO path already works. On the YES path there is room for exactly one more question, and after it the dolphin and the frog must land in different pens. Which question should the machine ask there?
Why this matters
Choose the test that splits the possibilities
Take your time reading. There's no rush at all. Use the picture on the side to help it make sense, then tell me what it's really asking.