Bit of a laugh? It's a gas, man! (2-2)

I believe the answer is:

he-he

'bit of a laugh?' is the definition.

'a gas man' is the wordplay.
'a gas' becomes 'he' (chemical symbol for Helium).
'man' becomes 'he'.
'he'+'he'='HE-HE'

'it's' is the link.

(Other definitions for he-he that I've seen before include "Amused expression" , "Sound of laughter" .)

I've seen this clue in The Guardian.

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