Mergers are one of the most common problems in EyeWire. Mergers are created when either the AI has included pieces from two different cells in a single segment, or when players mistakenly add a segment that does not belong. When the AI includes pieces from two different cells in a single segment, there is no way for the player to separate it into two segments, so they must learn to work around them. For smaller mergers that do not exit the cube a player may ignore them and continue their trace as normal. For larger mergers and/or mergers the exit the cube, the player may leave out the segment with the merger and continue their trace as normal.
In the event that the players create a merger, scythes or an admin is needed to remove it.
For varying reasons the AI can create mergers. It can be because of a misalignment, because of a damage in the neuron that the AI navigated through wrongly or because in the parent cube players created a merger and the AI created both the correct and the merger paths in the child cube creating thus an AI merger. In that last possibility removing the merger from the parent cube may not also remove it from the child cube, so an admin needs to remove it from there as well.
Misalignment AI mergers
Sometimes misalignments in the 2D slides can cause the AI to get confused and create a seed merger.
No-Borders AI mergers
There are spots inside the dataset that for whatever reason the neuron(s) were damaged and create "no border mergers" meaning that the borders between them are either damaged or gone and so the AI thinks that whole thing to be one single neuron when in fact its two different ones (or even possibly more than 2)
Player made mergers
Players can also create mergers even when there's not an AI merger that can mislead them into tracing a wrong neuron/segment(s). Be it misalignment(s), no-borders (usually shown as pure white in the 2D), fuzzy, unclear borders and so on. There have been a couple of isolated cases of players who traced everything in a cube on purpose. They were caught and "gifted" by the GrimReaper with -10,000,000 points and subsequent removal from the game.
This is a good example of a no-borders merger created by players. The circled piece in the image is to show where the merger is. It is usually presented in extremely white in the 2D and such segments must never be added even if they make a bouton/branch/nub/etc rounder and fuller as they do not belong and may lead to larger merger creation.