Intrusiones (Intrusions) are Adornos where you put your foot or leg between your partner's legs. Sometimes this is just a brief kick. Sometimes you'll use your foot or leg to push against one of your partner's feet or legs. When beginning tango the man does the intrusions but as dancers become more advanced women may do them too.
(from Larry (http://home.att.net/~larrydla/basics_5.html))