How to respectfully handle friends with gross habits?

This is both a rant and a need for advice.

My friends are really great people I enjoy time with but I cannot handle being at their house. I already knew previously that they are dog lovers and don't mind dog hair and drool all over the floor furniture. Okay. I get it. That happens sometimes. I can wear slippers and wash my clothes after leaving.

When I went over there today, I played with my friends guinea pig, and upon entering her room, there is guinea pig turds scattered on the carpet. I warned my friend she was about to step in it and she was like no big deal, picked it up and threw it elsewhere in the room, then proceeded to sit on the bed and watch tv. Mind you, yes they have electricity and running water there.

I cannot fathom how anyone thinks that is okay or normal and not disgusting. There is nothing wrong with me for not wanting to step in feces. I've had pets, and I so my best to clean up their feces or urine messes after I play with them.

I tried to hang out outside of the house, but nobody wants to go to the theatre without the serving of popcorn, and it's too cold to do anything outside right now. How can I avoid going to their house without seeming rude? Especially when my husband is best friends with the man.