In many big cities, it's impossible to live without encountering a mice or a rat at some point. They're tiny, fast, nocturnal and have mastered years of co-habitation with humans. They can enter your apartment through a hole the size of a quarter, sometimes even a dime. And once they're there, they get cozy...
One mouse can quickly turn into a family if you're not careful which means if you go to get a glass of water in the middle of the night you might be met with a party of baby mice hanging out on your stove. Snap-traps are the most efficient and humane method for controlling a rodent problem, and if you're scared to kill them you should know they're defecating all over everything you own and can, in anything from a normal to severe infestation, hang out on your bed. Just let that sink in and buy some snap-traps ASAP.