Final answer:
The two types of devotional service that are rarely seen are Atma-nivedanam, meaning self-surrender, and Sakhyam, considering the Lord as a friend. These require a high degree of spiritual realization, making them less common among devotees.
Step-by-step explanation:
The question pertains to the nine forms of devotional service in the context of Hinduism or Vaishnavism, which is part of the religious studies segment of social studies curriculum. According to the Bhakti tradition, there are nine primary forms of devotion known in Sanskrit as Navavidha Bhakti. However, two of these forms are less commonly practiced or 'rarely seen.' These are (1) Atma-nivedanam, which means full self-surrender, and (2) Sakhyam, which refers to considering the Lord as one's best friend.
Atma-nivedanam involves a total giving up of oneself to God, which is a very high state of spirituality not easily achieved. Similarly, Sakhyam requires an intimacy and level of personal closeness with the divine that many devotees may not feel qualified to claim. These two types of devotional service demand a high level of spiritual realization and commitment, which makes them less common compared to the other forms such as hearing and chanting the names of the Lord, which are more accessible to the average practitioner.