This has always been a hotspot for me, but have never been able to get around to making it happen IRL. Well, now that has kind of changed, but my pet has a severe gag reflex to anything in her mouth. We (I) have started training her, slowly for now. I have her bite down (gently) on a pen or pencil, held like a horse's bit, across her mouth, for five minutes at a time. The first time she struggled greatly. We have only done it a few times, but after the last session her comment was "are you sure that was a full five minutes?" She's a very good girl. She wasn't very interested in gags to start with, but her greatest pleasure is pleasing me. I showed her pictures of spider gags and she went "ooooh!" with excitement. I can hardly wait for the day, no matter how long it takes.