The physical parameters that affect the formation of Pele's hair and Pele's tears during lava fountaining are discussed. Experiments on ink jets produced from a nozzle under different Weber number ( We) and Reynolds number ( Re) show the following results: if ( Re) is relatively large compared with ( We), an ink droplet is produced. However, if ( Re) is relatively small and ( We) is large, the spurting ink becomes thread-like. I define the Pele number ( Pe) as ( We)/( Re), which is expressed as ρ ν η/ρ0 σ, where ν is the spurting velocity from an erupting vent, η and σ are viscosity and interfacial tension of the erupting magma, and ρ and ρ0 are density of air and magma. The experimental results from ink jets suggest that Pele's hair will be produced for larger ( Pe), while Pele's tears are very likely produced for relatively small ( Pe). I conclude that Pele's hair could be produced when the spurting velocity of erupting magmas is high, and Pele's tears when it is relatively low. As an additional point of interest, the similarity of SEM photographs of the characteristic shape of Pele's hair to those of the failed products of commercial glass fibre are shown.