Which Letter

[Puzzle Prime]

Which letter is encoded in this puzzzle?

[Professor Venturer]

It spells out “puzzle”. The letter must be Z because you spelled the word with a third z.

[Puzzle Prime]

You got the clue Professor. Spell out each of the shown items and you will notice something about their letters.

[Professor Venturer]

I already did! I noticed the pattern:

aPPle

vacUUm

piZZa

griZZly

baLL

trEE

[Puzzle Prime]

That’s right. Each box extracts the repeating letter from the corresponding word. Then, when you combine the 6 letters, you get PUZZLE, and its outer box yields the letter Z.