Cat sudoku tips and tricks

The fewer squares a color region has, the fewer places its cat can go. A one-square region is a free cat; a two-square region already tells you a lot about its row or column.

Every cat rules out its whole row, its whole column, the rest of its region and the eight squares around it. Mark all of them with X straight away. Crossing out costs nothing, and the X marks make the next move easy to see.

After each cat, scan the rows, columns and regions. Any of them with only one open square left has found its cat.

If every open square of a region lies in the same row, that region's cat is in that row. No other region can use the row, so cross out every other square in it. The same works for columns.

Scale the last idea up. If two regions both fit entirely inside the same two rows, those two rows belong to them and every other square in those rows is out. Three regions inside three rows or columns work the same way.

Imagine a cat on a square. If that cat would touch, or share a row or column with, every remaining square of some other region, that region would have nowhere left for its cat. The square cannot hold a cat: cross it out.

A wrong cat costs one of your three lives, but an X costs nothing. When a square is only probably right, keep reasoning until it is certainly right, and use X marks to test ideas.

The cross-out hint shows a square that cannot hold a cat without giving any cat away, and you get three per puzzle. Use those before Hint, which places a whole cat for you. A solve without Hint counts as perfect and earns bonus XP.