It is impossible to tell with the naked eye if a nit is dead or alive, but our studies have shown that the nits die when treated with Licefreee Spray. That being said, all of the nits have to be saturated with the treatment for the length of time recommended in the directions in order to die. There is a possibility that one was missed. Also dead nits will not fall off the hair follicle, they will stay attached and grow out with your hair if you do not remove them. We are happy to see it sounds like you did everything correctly and you were successful in ending your head lice infestation!