|“||Fire a shot that causes enemies to run out of cover. The shot is easy to hit with, but does reduced damage.||”|
– In-Game Description, XCOM: Enemy Unknown
A Flush shot receives a +30 Aim bonus but only inflicts 50% Damage. Similar to the Suppression ability, it does not impose a turn cool-down with use but instead expends a greater-than-normal amount of ammunition – specifically triple that of a standard attack. Note that the shot does not have to hit in order to force the target move; even a missed shot will flush the target out.
The new location selected by the target unit will be random, and is generally not dependent on the direction of the attack. The target may move out of cover into an open space, into better cover than they had before or even end up retreating outside of your squad's visibility area altogether. On rare occasions the target may teleport through one or more walls into a completely different area (presumably a bug).
Conversely, some enemies may sometimes not reliably be forced to move at all (though they will still take the attack damage if it connects), which seems especially applicable to flying units such as Floaters. It is currently unknown whether this is by design or is an implementation bug.
If the enemy does move, it will trigger as per normal movement rules any applicable reaction shots from soldiers on Overwatch (including via Squadsight), soldiers who are currently suppressing the target, or even Close Combat Specialists who are in range.
This ability requires the use of a rifle or shotgun type weapon; it does not work with a pistol. If you plan to use an Assault soldier as a Covert Operative later, he won't be able to use Flush while on Covert Missions due to them only having pistols to "easily conceal firearms with a low profile". For this lone Assault, it is absolutely worthwhile to choose the Rapid Fire ability instead, which is not just the only one of the two which works, but actually is quite helpful.