A blank cell touches no mines, so the game opens all eight neighbors for you and keeps opening any new blank cells it finds until numbers stop it.
When you reveal a blank cell, the game reveals its neighbors automatically. If any of those are blank too, it opens theirs, and the opening spreads outward until it reaches numbers.
Why it happens
A blank cell has no mines around it (what the numbers mean), so every cell touching it is safe to reveal. The game does that work for you, which is why one click can open a large area.
Where the opening stops
- At numbers: numbered cells are revealed, but they do not spread further.
- At flags: a flagged cell is left alone, even if it is safe.
Your first click always lands on a blank cell, so every game starts with an opening like this.
Using the opening
The edge of an opening is where the information is. The Minesweeper tips guide shows where to start reading it, and how to play Minesweeper has the full rules.