Chained boxes

Two boxes joined by a line are a chained pair. They are the mechanic that turns an easy-looking tray into a real puzzle, because they tie two columns together. Chained boxes first appear in level 5, Mini Burger.

The rules

• You can only take a chained pair when both boxes are in the front row at the same time.
• Taking one takes both, so you need two free slots.
• The pair moves into two neighboring slots. If your free slots are not next to each other, the boxes already in the nest slide over to make room.
• In the nest they stay chained: if one half sends all its ants first, it waits with a tick until its partner is done, and they leave together.

Why they are hard

A pair whose halves sit at different depths cannot be taken until you have dug both columns down to it. That forces you to take whatever is in front of them, even boxes you would rather leave for later. And because the pair occupies two slots until both halves finish, a pair with one buried color can block two slots for a long time.

Common mistakes

• Filling the nest just before a pair reaches the front, then having only one free slot.
• Taking a pair as soon as it is available when one of its colors is still buried.
• Digging one column toward a pair and forgetting the other half is three rows deeper.

How to plan for them

When you see a line between two boxes in the back rows, count how many taps each column needs to bring its half to the front, and use those taps on boxes that are useful anyway. Aim to have two free slots on the tap the pair becomes available. If one half's color is still buried, it is often better to leave the pair at the front and take something else first.