Locks and golden keys

Some boxes in the tray carry a padlock. A locked box cannot be taken, and while it sits at the front of a column, nothing behind it can be taken either. The keys are golden 2×2 blocks buried in the picture. Locks and keys first appear in level 6, Onigiri.

The rules

• A key comes out as soon as any side of it is exposed, that is, when the ants have eaten a block next to it.
• It flies down to the tray and opens the frontmost locked box: the one in the shallowest row, and the leftmost if several share a row.
• Keys are not eaten by any color, so you never need a box for them.

Why the depth of a key matters

A key near the edge of the picture comes out early, so its lock matters early. A key buried in the core only comes out near the end, and its locked box blocks its column for most of the level. In chapter 2 this is used on purpose: levels with a hard ending often hide their keys in the middle of the picture.

How to play locked levels

• Before your first tap, find the keys and note which colors surround them.
• Send those colors early; every block around a key is worth more than a block elsewhere.
• Avoid digging a column down to a locked box while its key is still deep. A lock at the front freezes the whole column.
• If a locked box is stuck at the front, work the other three columns toward the key.