With the rapid increase of students majoring in computing, undergraduate teaching assistants (UTAs) or have become a key resource for managing large courses and assisting students. Understanding the pedagogical practices employed by UTAs is essential for improving tutoring quality and meeting student learning needs. Our research aims to explore the pedagogical practices UTAs use during office hours and examine how they implement these strategies. To investigate these practices, we conducted an ethnographic study with seven UTAs, observing them for 37.5 hours in 50 tutoring sessions during office hours and documenting their interactions with students. Our study revealed that UTAs employ six pedagogical practices: asking open-ended questions, direct manipulation, prompting, referencing resources, explaining, and expressing affect. Tutors tended to rely on explanations, questions, and references to resources to support concept understanding, and hands-on directing and expressions of affect for debugging. Our work offers valuable insight into effective tutoring strategies that can benefit novice and experienced tutors.