Considering Games with the broad definition proposed by Juul (2010), consequences outside of the magic circle can be negotiated. This definition opens up the possibility to define serious games-games developed with a utilitarian goal in mind-in addition to fun. The entertaining and utilitarian objectives may however be contradictory, leading serious games to be, more often than not, less than optimal in at least one of the two dimensions. Another way to play with the boundaries of games is to consider pervasive games, which include alternate reality games, and cross-media games (Montola, 2005). We question here the limit between game, play and toy in the context of a mixed reality serious game. 'Pangu' is a game designed for undergraduate students, with biochemistry as the utilitarian objective, and the origin of life as a game theme. The students are asked to play the game on their smartphone, which in turn asks them to build molecules with a tangible balls-and-sticks model typically used in chemistry classes. Pictures taken from the models allow users to 'scan' these models and progress in the game. The use of the game was observed in four opportunities. An unanticipated observation is that, in addition to expected behaviours, some students briefly used the models like a toy rather than in the context of the game. It is therefore tempting to speculate that the pervasive nature of the game is blurring the game/non-game boundary and, in the context of this serious game, opens a door for fun. Some situations can be intuitively identified as play without any further analysis. Many situations are, however, more ambiguous and require a definition to be correctly characterized. Interestingly, these situations allow us to test our understanding (and associated definitions).