Assertion: octopus's tentacle | /r/CapableOf | act as rudder
Facets:
value: to control the direction of swimming
type: PURPOSE
Source sentences:
text: They flap their fins (the ear like structure found on either side of their head) for propulsion while the tentacles act as a rudder to control the direction of swimming.
text: While the flapping fins are used for propulsion, the tentacles act as a rudder to control the swimming direction and are how the octopus crawls along the seafloor.