Begin To Understand When It Becomes All The Rage

[gardenwise]

Enter Further Question Details Here...

[scorpiojo]

Is there a theme? Letter count?

[Tilly2]

Take in?

[cashier]

Catch on?

[gardenwise]

Thank you, cashier, that fits!

[Fibonacci]

Judging by this post
https://www.theanswerbank.co.uk/Quizzes-and-Puzzles/Question1657315.html
The question comes from Liz's quiz
Closing date 13 July
Question 2a
2A BEGIN TO UNDERSTAND WHEN IT BECOMES ALL THE RAGE(7,2)
Apparently to rhyme with
2B WHAT ARE STEWART WHITE AND PEEL (6.2.5)

[fiction-factory]

catch on is 5,2 rather than 7,2 though but gardenwise said it fits.
Odd.

[fiction-factory]

Probably is Lizzie's Quizzes though as gardenwise has posted from these before
I wonder what the answer to this one was https://www.theanswerbank.co.uk/Quizzes-and-Puzzles/Question1554942.html

[fiction-factory]

Answer does end in ON though.
If clue were BEGINS TO UNDERSTAND... then I'd say COTTONS ON

[JJ109]

or "catches" on FF!
Probably gardenwise mentally adjusted cashier's answer!

[fiction-factory]

Yes, must be "catches on" but clue doesn't see quite right does it- seems to me it should say "begins ...