Ropes are poisonous yellow snakes about 6 feet long. When a warm blooded creature (or other heat source) enters a room with ropes, roll a die for each rope in direct line of sight of it. On a roll of 1, the rope notices the heat source. On any other roll, it ignores it for the time being. If there is more than one source of heat in the room, 2 means it charges the second, 3 means it charges the 3rd, etc.
Ropes will generally move around randomly at a speed of 3, until they notice a source of heat, which they will charge at in a straight line at a speed of 12. They can be fairly easily dodged if a character sees one coming, as they are unable to stop once they start moving, and will continue in a straight line for another ten feet.
When characters enter a room with ropes, assign a number to each heat source in the room. At the start of each turn, roll one die for each rope. The rope will attack the heat source corresponding to its roll. If the roll is invalid (a roll of 5 when there are only 4 heat sources), the rope does nothing. If there are more than 6 possible targets, use two dice, and re-roll invalid rolls until the rope attacks. (It is unlikely that even a rope could miss 7 or more targets...)