Say == think

Natasha: Fluffy ruined my flowers once again!
Zack: Fluffy, the neighbor's cat?
Natasha: Yes. This is the third time this month.
Zack: Why don't you tell the old lady?
Natasha: I already did, but it doesn't make any difference. I don't know what to do.
Zack: I say we get a dog. A very big dog. It'll scare the cat away.

I'd like to know here what meaning "say" has.
Thank you in advance for your help.