Ingestible sensors, such as capsule endoscopy and medication monitoring pills, are becoming increasingly popular in the medical domain, yet few studies have considered what experiences may be designed around ingestible sensors. We believe such sensors may create novel bodily experiences for players when it comes to digital games. To explore the potential of ingestible sensors for game designers, we designed a two-player game - the "Guts Game" - where the players play against each other by completing a variety of tasks. Each task requires the players to change their own body temperature measured by an ingestible sensor. Through a study of the Guts Game (N=14) that interviewed players about their experience, we derived four design themes: 1) Bodily Awareness, 2) Human-Computer Integration, 3) Agency, and 4) Uncomfortableness. We used the four themes to articulate a set of design strategies that designers can consider when aiming to develop engaging ingestible games.