what is this

i have always been curious about what this is on the left side of his nostril, i believe he has always had it.

I found this whilst cleaning out my two boars. It’s pretty hard, but a bit sticky on the outside. What is it?

I have 2 Male guinea pigs and we were just checking one to make sure he doesnt have any bumps. And as we were checking him (Charlie) and we found these 2 marks next to his back legs. Does anyone know what these are?