I think your botty is prolly more desensitized than your nose or tongue, seeing as it is designed to push nasty stuff out.
Never felt anything nasty from plugging apill, other than the discomfort of the intial plug...
in aus we call it shelfing a pill... if you shelf a pill up your arse the effects are alot alot alot stronger!
a guy i used to go raving with did it and it made him ahve a heart attack from just an average pill! he does havea heart problem but no other pill taken orally has being as strong and it was only an average pill according to everyone that took it orally!