Yes, it's probably just a lack of practice. Sounds you are not used to recognise. (I understand because we I speak English I fail to hear the letter H because we don't pronounce it in French) For me, "les gens" is miles apart from "les ans". (The first one sounds "lè jen" and the second "lè zen".) G is pronounced with top teeth almost touching bottom teeth in mock growling look. Z is a tongue only noise. Train your ears, then your tongue ! Good luck.

Jacob, that's a tricky one! Try listening to this video, then do the exercises below (the last one at the bottom) - maybe it will help! :) http://www.youtube.com/watch?v=w2Y_pmlvw8k http://phonetique.free.fr/indexphoncons.htm ... And one more link if you really want to hear those sounds even more: http://www.prononcer.net/consonnes-z-j-exercices-mp3-telechargement-gratuit