Well a couple things come to mind.....
First off, a snake would have to travel a long long way through a sewer system in order to make its way into house plumbing. Even at that, kitchen plumbing is only 1-1/2 inches ID and bathroom sink is 1-1/4 ID. So the overall diameter of the snake could be no larger than those size pipes if it was to ever make its way into a sink drain. Not considering the fact that snakes have to slither in order to move so a 1" snake would have a tough time moving inside a 1-1/2 pipe. And.....a snake small enough to make its way through those pipes wouldn't be very long.
Also, If the house is on a septic then there's no way a snake could make its way in the pipes unless it crawled down the roof vents and moved down and backwards up the street ell fitting which would instead point the snakes direction downward further into the piping instead of up around the tight turn and into the house.
Lastly, if the sink has the normal drain then there's no way for a snake to get through the small drain holes you see when looking down into the sink. Even garbage disposal plumbing openings arent direct shots up into the sink otherwise they wouldnt chew up the food before it made its way down the pipes.
So in short.....I highly doubt there's a snake in your house unless you have some seriously sketchy plumbing issues. Especially the dangerous types you mentioned which are very unlikely to leave the safety of their natural habitat and venture into foreign area's like a house.
I'm sure either something else made its way in like a bat or small bird or mouse through a window or vent you didnt know was open.....or someone broke in or came over while you were gone.
