When a person with crabs,pubic hair comes in contact with a persons actual
head hair (this person must have
nits) after these crabs and nits mate this produces
nids.
Basically you have aids in your hair.
Harry has been poking sally and stops to scratch his head making the
crabs off sallys pubic hair touch the hair
on his head, outcome :
ewww man you have
nids !