I was going through the "Red Book of Magic", the official spell compendium for Runequest, and was surprised to see it has  a spell called "Swallow".<br/><br/>The effect being.<br/><br/>"Any living being swallowed by the caster dies immediately."<br/><br/>Sadly theres no struggle mechanic, but theres a couple of monsters in Runequest that also have a swallow feature, so I suppose you could use their escape rules for it.<br/><br/>Its also hammerspace, but you could always hombrew it to pretend its not if you want to rp a belly.<br/><br/>"the caster doesnot suffer any effects from using this spell, such as increased<br/>SIZ due to the amount swallowed."<br/><br/>Seems like  it could be useful for a vore themed campaign if you don't want dnd.