Venomous snakes use highly specialized teeth, so-called fangs, to kill living prey items. The evolution of these fangs and that of the associated venom-producing and -delivery system has been the subject of continuous research (e.g., Kochva 1978, Kardong 1982, Knight & Mindell 1994, Jackson 2003, Fry et al. 2008, Vonk et al. 2008). In addition to the evolutionary origin of tubular fangs, their ontogenetic formation has been studied as well (e.g., Tomes 1874, Bogert 1943, Klauber 1972, Lake & Trevor-Jones 1987, Lake & Trevor-Jones 1995, Jackson 2002). While our knowledge has significantly increased thanks to the integrated evaluation of palaeontological, morphological, physiological, molecular and other data, some details still remain unresolved. One such remaining problem concerns the timing and regulation of fang replacement, i.e., when and how a functional fang is replaced by a new fang. This topic has been briefly touched by Jackson (2007). Snakes replace their teeth, including the fangs, regularly and continuously, therefore there is always a number of replacement fangs posterior to the functional one. The maxilla typically has sockets for two fangs in lateral versus medial positions. At any given time, one would expect one fang to be solidly fused (ankylosed) to the socket and the other more or less loose and in the process of either attaching or being shed. However, as a functional safety factor, the phase when both fangs are ankylosed should overlap to some degree, avoiding a time window where both the replacement fang and the one in the process of being shed would not be fixed to the upper jaw. According to Klauber (1972), this period of overlap must be short, since two functional fangs on one side (i.e., both are firmly set in neighbouring sockets) are observed very infrequently. Here we report for the first time on the fang configuration at the stage around fang replacement, using CT-data with 3D visualisation. During our field expeditions in the Democratic Republic of the Congo, two specimens of venomous snakes were found where ‘double fangs’ were visible on one side of the maxilla. We use this term to describe the stage during fang replacement when both fangs in both sockets are ‘out’ and clearly visible. However, we could not test whether the new fangs were fully functional, since the soft tissues and presence of venom in the venom canals were not examined.