# Rolling boulder trap

^ rolling boulder trap 

Generates

level 2+

Effect

Rolls boulder, causes damage

A rolling boulder trap is a type of trap that appears in NetHack, and causes a boulder to roll towards you and hit you.

Contents

1 Generation
2 Description
3 Removal
4 Strategy
5 History
6 Messages
7 Variants

7.1 SLASH’EM
7.2 UnNetHack
7.3 xNetHack

8 References

Generation
Rolling boulder traps can generate as early as the second floor of the dungeon.
Two rolling boulder traps are generated in fixed locations on the locate level of the Archeologist quest, and a third is generated in a fixed location on the goal level.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.
The "boulder room" themed room has a 3⁄10 chance of generating a rolling boulder trap on each floor space in the room. 

A new variant of the Big Room is added that contains a maze level with 3 to 5-square wide corridors and 1-square wide walls made of boulders; the random traps are all rolling boulder traps.
Description
The rolling boulder trap consists of a trigger square and a single boulder, usually placed out in the open and in the same room as the trap, and requires a clear path for the boulder in order to trigger.[1] If you or another monster steps on that square, the boulder will roll to the opposite side, usually hitting whoever triggered it along with any other monsters in its path;[2][3] being hit by a boulder deals d20 damage. The boulder will stop rolling if it runs into something that obstructs it - a boulder that crashes into another boulder will send it rolling onto the launch square and wake up sleeping monsters within a 10-square radius.[4]
As long as the boulder is on a launch square when the trap activates, the trap can set it rolling and will do so on repeated triggers;[5] the boulder will always stop at the other launch square on the opposite side unless obstructed. A boulder trap will not trigger its boulder to roll if the path is blocked by a wall, or the boulder is moved off the launch square by anything other than the trap itself. A boulder set rolling by this trap can disappear midway through rolling if, for example, it fills a pit, hole or trap door, or it is caught by a giant that was in the way. Stepping on a rolling boulder trap that cannot trigger a boulder will cause the trap to disappear with no other effect.

Removal
Rolling boulder traps can be destroyed by activating the trap when there is no suitable boulder on a launch square.[2][3]  You can either move the boulder out of line or else shatter it, e.g. with a force bolt or pick-axe.

Strategy
Rolling boulder traps are among the many threats posed to an early character, and are especially so for any starting kittens or little dogs. You can often spot a rolling boulder trap by the seemingly incongruous placement of a boulder in a room. 

History
The rolling boulder trap is introduced in NetHack 3.2.0.

Messages
Click! You trigger a rolling boulder trap!
You triggered a rolling boulder trap.
Click! 

<monster> triggers something.
A monster triggered a rolling boulder trap.
Fortunately for you, no boulder was released.
There was no boulder in the launch spot for this trap, so the trap is destroyed.
You hear rumbling in the distance.
A boulder trap was activated outside of your sight range.
You hear someone bowling.
As above while hallucinating.[6]
You see a boulder start to roll.
As above, but the trap's boulder was visible to you.
You hear a loud crash as a boulder sets another in motion.
A boulder hit another boulder, causing the first boulder to stop and the second to move.
Variants
SLASH’EM
In SLASH'EM, two rolling boulder traps appear in set locations within the Lawful Quest.

UnNetHack
In UnNetHack, 10% of rolling boulder traps will also generate an archaeologist corpse, a bullwhip, and a fedora with a 1⁄3 chance.

xNetHack
In xNetHack, the player does not trigger rolling boulder traps unless actually standing on the ground, as with monsters triggering the trap. Rolling boulder traps also have a chance of generating an archaeologist corpse, a bullwhip, and a fedora with a 1⁄3 chance.

References

↑ src/trap.c in NetHack 3.6.6, line 398

↑ 2.0 2.1 src/trap.c in NetHack 3.6.6, line 1534: Handling for players activating the trap

↑ 3.0 3.1 src/trap.c in NetHack 3.6.6, line 2690: Handling for monsters activating the trap

↑ src/trap.c in NetHack 3.6.6, line 1982

↑ src/trap.c in NetHack 3.6.6, line 1771

↑ src/trap.c in NetHack 3.6.6, line 1815

</monster>