I use aspen, and you can see if there is aspen stuck in their mouths. It's happened to my boa twice and one of my ball pythons once. It sticks out the side or front a little, and in my boas case, he couldn't realign his jaw correctly.
If you feel the need to pry the mouth open, which I don't think is necessary, get a Q-tip and use the "pole" part of the Q-tip and roll it inwards, their mouths will open...not usually willingly. Make sure you have a good grip on the head without blocking the airway on the throat.
To remove aspen I just use tweezers lol.