In their Perspective, Zimmerberg and Chernomordik discuss the study by Rigoni et al. In the same issue that shows how the lipid products of a phospholipase present in snake venom reproduce the known paralytic effect of the lipase itself on presynaptic action in the neuromuscular junction. The lipid products shift the curvature of synaptic membranes toward or away from intermediate states of membrane fusion. This suggests a hemifusion intermediate state in synaptic vesicle release and explains the existence of rapid and spontaneous neurotransmitter release from vesicles.