A trap (or 'mark') is achieved when all the adjacent intersections of a piece are occupied by opposing ships. Note that the kraken cannot be one of the pieces used to surround and a surrounded group is not considered trapped. There is no capturing in Mur. When a ship is in a trap, the owner of the ship must remove it from the board. The withdrawn ship then becomes an ‘off-board’ piece. A player may have any number of off-board pieces at any one time. Any off-board piece may be entered back into play by simply placing it back on the board on any unoccupied intersection. However, when the kraken is trapped, it is not placed off the board; it is placed upon the center intersection of the board as a reset (see completing the game). Note that it is possible to trap two ships simultaneously as long as the ships are alone and not part of a group.
When an unoccupied intersection is surrounded by ships of the same colour this is called an eye intersection or ‘eye’. An eye is formed from the withdrawal of a trapped ship or may be formed just from the course of play. Placing, moving, or knocking your own ship (or the kraken) into an opposing eye is not allowed unless it results in the immediate trap of an opposing ship forcing the next play to be a withdrawal by the opponent. This kind of situation is called a 'mixed traps position'.