The attacker chooses a tiny target message that differs by one byte.
The attacker chooses a nearby message
The original toy message says pay equals 10. The target says pay equals 90.
Target bytes
The target plaintext bytes are 0x7061793d3930. Only one byte differs from the original.
target=0x7061793d3930
The changed byte
The byte for 1 changes to the byte for 9. In hex, 0x31 changes to 0x39.
0x31→0x39
Summary
The target is exact and small: change pay equals 10 into pay equals 90.
changed bytes=1