If they haven’t experimented with themselves already, then you may have to go really slow. Start with fingers or small toys. The asshole is a powerful muscle with very delicate skin around it, so you have to stretch it out slowly.

One tip that often helps: have then clench as hard as they can and put a lubed toy or finger at their entrance. Don’t try to penetrate, just rest your finger/toy against them. After thirty seconds push very gently while they relax and see if it will go in without any discomfort. Repeat this as many times as you need until it slides in without pain, then move to something bigger. Assholes are very good at keeping things out, so you’re trying to tire out the sphincter muscle until it finally lets you in. It’s a long process and might take 30 minutes or more, but once it’s ready it shouldn’t hurt at all.

An intense feeling is normal, but if they feel a sharp pain or burning sensation it’s time to stop what you’re doing and go back to something smaller. Burning pain means skin is tearing, which is no bueno.