Draw a closed loop into the grid that runs horizontally and vertically and passes through each cell at most once. The loop cannot pass through cells with numbers. The loop cannot touch itself, not even diagonally. The numbers indicate how many horizontally, vertically and diagonally neighbouring cells are used by the loop.
(Rules and example from WPC 2019 IB)
- Bosnian Snake: Draw a Snake, instead of a loop.
History of the puzzle
Serkan Yürekli named the puzzle in 2009 after the home country of Dragan Tolomanoski (Bosnia & Herzegovina), the puzzle's inventor. 
Full Bosnian Snake
First appeared on WPC 2016/Round 4 ("Full Classics" round). Author of the puzzle was Matúš Demiger (Slovakia).
Shade some cells to get a valid Bosnian snake solution:
Shade some cells in the grid to create a single one-cell-wide snake in the grid. The snake cannot touch itself, not even diagonally. The remaining (unshaded) numbers in the grid indicate how many of the 8 cells around it are occupied by the snake. The position of the head and the tail is unknown.
(Rules and example from WPC 2016 IB)
Appearances in the past WPCs
- WPC 2019/Round 10 by Sebastian Matscke
- WPC 2018/Team Round 3 (part of a combination puzzle) by Jiři Hrdina
- WPC 2017/Round 7 by Prasanna Seshadri
- WPC 2016/Round 4 (Full Bosnian Snake) by Matúš Demiger