I had to force Amy to open her mouth just to get water into her last week. It was something that I've never had to do before but it was actually quite easy. Use a rubber spatula or credit/gift card (I used the latter) and gently prise the mouth open. You may need to get someone to hold the cham still though or wrap him in a towel. Exercise caution when administering food or fluid in this way as squirting too much in at once may cause the cham to aspirate it instead of swallow.