* Dead octopus or squid can be purchased from some fishmongers and so the body shape, the remarkable eyes and siphons as well as the tentacles can be counted, measured, observed and drawn. Older pupils can cut it open and investigate the musculature of the tentacles and the location of the ink sac. Plastic sucker hooks or domestic plungers - or "pop guns" with sucker "arrows" - can be used to investigate suction pads. There's scope for investigation here, even at primary level: the length of time a sucker remains fixed, the effect on its effectiveness of fixing it to different surfaces or suspending different loads are just a few ideas.
* You can show that water supports heavy objects by hanging a brick from a Newton meter then lowering the brick slowly into a bucket of water while watching the scale. Then hypothesise about why beached whales don't survive.
* Pupils can explore the range of movements of their own arms easily, and link manual dexterity to the opposable thumb. The range or limitation of joint movement and the antagonistic arrangement of our skeletal muscles can be explored using model skeletons. At KS3 or 4, the relative positions of the pivot, load and effort in the body's different levers could be linked to the biomechanics of the octopus.
* Work on camouflage, warning colours and mimicry can extend the observations of rapid colour adaptation shown by the octopus too.