Leniting negation; chan before vowels and fh, cha before consonants.  The -n fuses onto a vowel or fh and strengthens to /N/ or /Nʲ/ according to the broad and slender distinction:
chan àrdaich mi /xa NaːRdɪç/
chan òrdaich mi/xa NɔːRdɪç/
chan ùraich mi/xa NuːRɪç/
chan èist mi/xa Nʲeːʃdʲ/
chan ith mi/xa Nʲɪç/

chan fhàg mi/xa Naːg/
chan fhill mi/xa NʲiːLʲ/

Blocked lenition with dentals (dntls):
cha dùin mi
cha naomhaich mi
cha tuig mi
cha leig mi
cha seas mi

Note that in some Hebridean dialects, especially Lewis, cha lenites all consonants except for dntls in irregular verbs:
cha dhùin mi vs. cha dàinig mi
cha dheasaich mi vs cha dug mi