Abstract: The experimental observation of nanojets formed by heating PbO-coated Pb clusters is reported. As the temperature increases the Pb core which has a lower melting point melts first, then expands, breaks its oxide shell and finally forms a nanojet with a condensed trail in the shape of a tadpole. The temperature-dependent Raman spectrum indicates that the nanojet formation is closely related to the temperature, and essentially to the internal pressure of the coated cluster. The pressure inside the shell comes from the inner core's melting and its confined volume expansion, resulting in explosive release of the high pressure.