© 2013 American Institute of Physics. When becoming a member of a community of practice, a novice must adopt certain community norms to participate, and these include the social norms of the group. Using the analytical perspective of Legitimate Peripheral Participation in a Community of Practice, this paper explores the social role of cookies as agents for community participation and membership in a physics research group. We analyze data from an ethnographic case study of a physics research group weekly research meeting. The mentors bring cookies to each meeting and view the cookies as a token of appreciation for the graduate students’ work. These cookies take on a subtler role of initiating guests and students into scientific conversations and participation. Via the cookies, members also share personal histories and stories that help members strengthen their membership. The study of social norms in this research group is part of a larger study of physics expert identity development.