How does one discern a calling to the vocation of religious life?

Approaching this from a Catholic perspective, I'd like to ask believers how they came to know that they were called to join the religious life (as a brother or nun), as opposed to the other vocations (priesthood, marriage, single life etc). Rephrasing the same question, what should a believer look for when discerning whether they are called to the vocation of religious life?