a word that begins with F and ends with CK

(1)I’m signing my dad’s cast
(2)Sure.
(3)What did I write
(4)Don’t worry
(5)I wrote something
(6)I’m sorry. That’s with me
(7)It’s a secret between everyone who sees it
(8)I need to know!
(9)It starts with an F and ends with a C-K