I have been having a similar problem with my juvenile pacman frog as well. Infact I have 4 in total and this is the second one that has done it, so I believe it is just a normal thing. One time my pacman was doing this and not eating the food I was putting in front of him when he was in the borrow. What I found to be the best thing to do in this situation is to get a small deli sized container and just fill it up a couple of centimeters with water. Then place both your frog and the prey item you are trying to get it to eat, and leave it alone. Usually after about 10-20 min it will eat. If not it might just not be hungry at that time, put him back and try again in 6 hours. By then he would eat.