I would much rather have a Bigfoot house slapping then the same Bigfoot knocking on wood.
That being said there are certain times of year when the feet will pull on themselves while slapping.
Similar to how a dog shakes it's leg violently while having its tummy scratched.
If you accidentally stumble upon a tugging slapper sequence proceed with caution.
Chances are good the Bigfoot will respond aggressively if interrupted.