Solving German whispers
Neighbors on a green line differ by at least 5. No digit is 5 away from a 5, so 5 never goes on a whisper. Every other digit is either low (1 to 4) or high (6 to 9), and the line swaps between the two.
Why it works
On the board above:
r5c4 has two neighbors on the line: r5c3 and r5c5. Each must differ from r5c4 by at least 5.
No digit is 5 or more away from 5, so r5c4 can’t be 5.
If r5c4 were 4, both neighbors would have to be 9. They share row 5, so they can’t both be 9. The same goes for 6, which would need two 1s.
So r5c4 can only be 1, 2, 3, 7, 8 or 9.
More moves
High and low swap
Every neighbor pair is one low digit and one high digit. Once you know one cell’s side, the rest of the line follows.
r2c1 is 8, which is high. So r2c2 must be low: r2c2 can only be 1, 2 or 3.
A low cell’s neighbor is high, so r2c3 is high. Then r3c3 is low and r3c4 is high.
The line swaps side at every step: low cells r2c2 and r3c3, high cells r2c3 and r3c4.
How to use it
Cross out 5
Every cell on a whisper loses 5 straight away.
Split high and low
Neighbors are always one low and one high. Find one cell’s side and the whole line follows.
Check 4 and 6
A 4 needs 9 on each side, and a 6 needs 1 on each side. Two neighbors that see each other can’t both be 9, or both be 1.
Use the partners
Each digit has only a few partners: 3 goes with 8 or 9, 7 goes with 1 or 2.
Partners on a whisper
Practice
8 boards. Each has one right answer, checked by our solver.
Loading the boards…
Try it in a real puzzle
Each of these starts with whisper logic.
Tips
Line up the sides
On a long line, color the low cells one way and the high cells another. The colors alternate.
A cell in the middle of a line
A cell with two neighbors on the line can’t be 4 or 6 unless those neighbors don’t see each other.
Watch the ends
An end cell has only one neighbor on the line, so it can be 4 or 6.
Count the lows
A box crossed by a long whisper can run out of low or high digits. Count them.