The Double-Cross in Dots and Boxes: All but Two

Taking every box you are offered feels right, and it is how most games of Dots and Boxes are lost. Strong players stop two boxes short.

Step 1 of 5

Take them all?
Red has opened the top row at its left end, and the bottom row is the only other chain. Watch Blue take all four boxes of the top row. Blue then has to draw another line, and every line left is in the bottom row, so Red takes all four of those. Of the eight boxes that were left, each player got four.
All but two
The same position. This time Blue takes two boxes, then draws the line at the far end of the row instead of taking the third. That line claims nothing, so the turn passes. Red takes the last two boxes with one line, a double-cross, and then has to open the bottom row. Blue takes all four: six of the eight boxes, instead of four.
Hand back two
Now you play it. The stars mark the bottom row, the chain Red will have to open.
Your move
Take all but two boxes of the top row, hand the last two back, then take the bottom row.
The last chain
Later in the same game, Red has opened the bottom row, and it is the last chain on the board. Do you take all four boxes, or all but two?
Question
Give two boxes the right way
Now you are the one giving boxes away. Only the left column and a 2-box chain at the top of the right column are left, and it is your move. Give Red the short chain, but think about where you draw: Red knows the double-cross too.
Your move
Give Red the 2-box chain in a way Red can't hand back, then take the column.

What you learned

Take all but two boxes of a long chain, then draw the line at its far end.
Your opponent takes the last two with one line, a double-cross, and has to open the next chain.
Take all of the last chain: there is nothing left for your opponent to open.
To give away a 2-box chain, draw the line between its boxes, so it can't be handed back.