Mines are twice as efficient. "A pink, volatile gas, found in the depths of some chocolate caves."
Mines are twice as efficient. "You're in deep."
Mines are twice as efficient. "Finally caved in?"
Mines are twice as efficient. "Pierce the heavens, etc."
Mines are twice as efficient. "Questionable efficiency, but spectacular nonetheless."
Mines are twice as efficient. "You've finally dug a tunnel down to the Earth's core. It's pretty warm down here."
Mines are twice as efficient. "These new state-of-the-art excavators have been tested on Merula, Globort and Flwanza VI, among other distant planets which have been curiously quiet lately."
Canola oil wells
Mines are twice as efficient. "A previously untapped resource, canola oil permeates the underground olifers which grant it its particular taste and lucrative properties."
Mines are twice as efficient. "Engineered from real human beings within your very labs, these sturdy little folks have a knack for finding the tastiest underground minerals in conditions that more expensive machinery probably wouldn't survive."
You need at least 15 mines to purchase the "Miner Grandmas" upgrade.
The ultimadrill upgrade's flavour text, "Pierce the heavens, etc." is reference to the anime Gurren Lagann , where lines such as "Your drill is the drill that will pierce the heavens!" are said several times.
It would cost a total 91.93 quadrillion cookies to get the 200 mines necessary for the "Coreforge" upgrade, the last 20 mines representing 94% of that total cost.
Never Dig Down is a reference to Minecraft, where digging straight down can lead to death by lava.
The upgrade "H-Bomb Mining" is a reference to "Operation Plowshare" - A series of experiments by the US military to find non-combative uses for nuclear weapons. Unsurprisingly, testing proved that nukes were good for many things, mining however not being one of them.