One letter, 3 rows
Find the one letter that finishes the word on the left and starts the word on the right. The same letter has to work in all 3 rows.
The letter in the gap is doing two jobs at once: it is the last letter of the word on the left and the first letter of the word on the right. Here it is P, giving MAP and POET, HOP and PEN, SHOP and PEA. The efficient way in is always the left-hand fragment, because a word can only end in a handful of letters, while lots of letters can start one. Build a short list of letters that finish the left-hand word, then test that short list on the right. With more than one row the letter has to survive every row, so a letter that clears the first row and fails the second was never the answer, however good it looked. Working the two sides in that order turns a search through the whole alphabet into a search through two or three letters.
What to say if they get stuck
- Start on the left of the first row. Say MA and try each letter on the end of it until you hear a word.
- A letter that works in one row is only a candidate. Carry it down to the next row and see whether it still works there.
- There are 5 letters that finish MA on their own, so test those first rather than working through the alphabet.