red thread

it would seem that 'to lose the red thread' is a German expression meaning to lose one's train of thought.
به نظر می رسد که "از دست دادن نخ قرمز" یک عبارت آلمانی به معنای "از دست دادن رشتۀ فکر" است.

سر رشتۀ بحث

نوعی بیماری است:
a disease of turf grasses caused by a fungus ( Cortecium fuciforme ) and characterized especially by reddish stromata on or in the pinkish web of hyphal threads