producing thrust causes an animal to move & a squid produces a stream of water out of its body that causes it to move ->  a squid produces thrust by pushing water out of its body  a squid produces thrust by pushing water out of its body & a rocket engine is used to produce thrust by pushing gases out at a high speed ->  a squid and a rocket engine both produce thrust  a squid and a rocket engine both produce thrust & producing something is a kind of function ->  a squid and a rocket engine both perform the function of producing thrust  a squid and a rocket engine both perform the function of producing thrust & if two things perform the same function then those two things are similar -> a squid is similar to a rocket engine