Whack-A-Grub - Gears of War: Ultimate Edition

Close all 4 E-Holes around the fountain in Fish in a Barrel without any Locust fully emerging - 10

Mission: Chapter 1, Act 3

After you find the dead bodies of Alpha Squad, you'll fight down the street towards a fountain, with 2 grenades and an ammo crate in it. Pick up the grenades to make 4, you received 2 at the beginning of the level. Selecting grenades and then aim at the holes as they begin to form, the game will point you in the right direction with "Points of Interest" (Y). You need to throw a grenade into the hole before any Locust come out, what it means before any of the Locust climb out and stand up. If you fail restart from the last checkpoint.

This achievement is a reference to the Whack-A-Mole Arcade Machines. Where the player has to whack the moles when they emerge from their holes.

Emergence Hole