Reference for Yoma 55:5
למימרא דעבודה תמה וזר חייב עליה מיתה בעיא פייס אין זר חייב עליה מיתה לא בעיא פייס והרי שחיטה שאני שחיטה דתחילת עבודה דיממא היא
The [reason is] as we have already stated. Are we to say that for a service which is complete, and for the performance of which a non-priest incurs the penalty of death, a count is required, but for one, for performance of which a non-priest does not incur such penalty, no count is required - but there is the killing [of the sacrificial animal]? - It is different wit that killing, because it is the beginning of the service of the day. Shall we say that only a complete service requires the count, but a service followed by another does not require it - but there is the smoking of the members and the fat-pieces? - That is the end of the service of the day.