To impale something on a pointed object means to cause the point to go into it or through it. Researchers observed one bird impale a rodent on a cactus. if someone or something is impaled, a sharp pointed object goes through them be impaled on sth (empaler, from impalare, from palus )
[ im-'pA(&)l ] (transitive verb.) 1605. Middle French and Medieval Latin; Middle French empaler, from Medieval Latin impalare, from Latin in- + palus stake; more at POLE.