Normal sudoku rules apply. The 9 blue circles must contain a set of the digits 1-9. Lines are hit point lines. The blue circles show the total of the line's sum which is made up from digits in their correct position along the line. (Eg a line reading 14325 would have the total 9 as 1 is in the first position, 3 in the third and 5 in the 5th but 4&2 are not correct being in the second and 4th position respectively). Digits may not repeat along lines. Some lines have a square at the end. These squares mark the position of the first digit in the sequence. For lines without squares, the solver must determine in which direction they go, but they must always start at one end of the line and finish at the other. White dots mark consecutive digits, not all white dots are necessarily given. The rat's nose contains an odd digit (this last rule does not appear on the card in the video!).