Messy person has kittens before hesitation (8)

I believe the answer is:

litterer

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'messy person' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see an association between them that I don't see?

'kittens before hesitation' is the wordplay.
'kittens' becomes 'litter' (I've seen this before).
'before' says to put letters next to each other.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'litter'+'er'='LITTERER'

'has' is the link.

Can you help me to learn more?

I've seen this clue in The Daily Express.

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