I love this questions. Ideal for Christmas fun time hour...
Because an octopus doesn't have tentacles. They are known as arms.
Tentacles are distinguished in this context as being longer than arms, with suckers at their tips only.
hmm, yes. but imagine if it were called eightpus??!!
err yes, you are right... so are 'they'...but the juvenile in me giggles at the phonetics
Lol. I often wondered this too. Then my mind gets all bound up in thought, next thing I know I am thinking Octopussy. Then I start thinking over and over then ...*poof* Barberella! This is what happens when I have too much butter before bed. LOL.
cheap christmas cracker jokes tells me it is still only january ;-))
respect, from robbie