Laugh sneeringly when the reins get tangled round a horse! (7)
I believe the answer is:
snigger
'laugh sneeringly' is the definition.
'snigger' can be an answer for 'laugh' (sniggering is a kind of laughing). I am not sure about the 'sneeringly' bit.
'the reins get tangled round a horse' is the wordplay.
I cannot quite see how this works, but
'horse' could be 'gg' (geegee or GG is a childish term for a horse) and 'gg' is present in the answer.
an anagram of 'reins' is 'snier' which is located in the left over letters.
This accounts for all the letters.
This explanation may well be incorrect...
'when' acts as a link.
Can you help me to learn more?
(Other definitions for snigger that I've seen before include "Disrespectful laugh" , "Laugh disrespectfully" , "Suppressed laugh" , "Gingers up to laugh in sly way" , "Laugh scornfully" .)