A web spelling of the Scottish/Northern Irish slang
boak (which occurs because "boke" looks like
how you'd spell it) which can mean either vomit or dry heave (
the dry boak).
On BBC Scotland when
Rab C.
Nesbitt asked, "Got a wee touch of the
boak, eh doll?" a lot of folks might have thought he said "boke" -- if they could understand his Glaswegian at all.