There are actually a lot of cognates.
apple - jabłko (not so visible)
milk - mleko
bread - chleb (think of "loaf", German "Laib")
water - woda
love - lubić (they have different meanings, but they are related)
cat - kot
mouse - mysz
lion - lew
Most of them are not as obvious as "crab - krab" but indeed there are more similarities than one might think at first glance.
Nay, a borrowing! I've been told crabs are not found in Poland; in fact, there are a few species, but crabs were not very well known traditionally in Poland, which is why the Latin 'cancer', referring to the zodiac sign and the disease, is represented by 'rak' (crayfish) in Polish.