Well, it came uninvited, and it continues to come inside uninvited, but a brown rat has frequented the house (both beneath and inside our living space) for the last two or three weeks. It scurries away when it detects movement or is frightened (and I can be similarly startled in return), but it has already aroused Mom’s ire after it did a number on a pack of soy sauce in the pantry. 

So we’ve battened down the hatches in the kitchen over the week, and we haven’t seen it (him?) inside that particular area since, but now it comes inside through an unenclosed space in the bathroom closet behind the shower. I’ve swept up its pellets from that area, but I’m still reluctant to have Mom sic a peanut-buttery trap on him. It seems inhumane, IMO, even if he is an undesired guest.

I’m going for a live trap, or even this DIY idea, instead.

EDIT: This is a rather dandy website (in Russian).