Some species of snakes carry horn-like appendages either on the snout or above the eyes. Interestingly, these structures have evolved independently in multiple clades of vipers (Viperidae). Pioneer herpetologists have speculated wildly on the function of these enigmatic appendages, but nobody has studied them in detail. In this project, I will test the putative role of rostral and supra-ocular horns in concealment, water uptake, mechanosensation and thermoregulation. To that end, I will carry out a combination of behavioural observations, visual modelling, vibrometry, thermography, (electron) microscopy, histology, µ-CT scanning and 3D image reconstructions, on a selection of specimens of different species. In a final step of the project, I will combine information obtained from the functional analyses with data on the distribution, ecology and natural history of viperid species (as available in the literature and online databases) to test ideas on the ecological drivers of horn evolution.