Definition of niggles:
(n) :
A minor complaint or problem.
(v) :
(intransitive) To dwell too much on minor points or on trifling details.
(v) :
(transitive) To use, spend, or do in a petty or trifling manner.
(v) :
(intransitive, chiefly UK) To fidget, fiddle, be restless.
(v) :
(transitive, obsolete) To trifle with; to deceive; to mock.
(n) :
(obsolete) Small, cramped handwriting.