A lot of the housemates this year (if not all of them) have clearly been avid viewers of the previous Big Bros. Thats not a bad thing but it does mean that they are much more aware of how the game works, how the public vote, how they are portrayed and what to expect from Big Bro.
It means they are a lot more careful about what they say and do. That pathetic argument over the rat was one example. IMO, some of the housemates (Richard in particular) thought the public would like them more if they showed how concerned they were over the rat's safety.
A lot of them are very careful not to say anything too outrageous or controversial, (although equally some of them lack the intellectual capacity to actually hold a contentious opinion on any relevant issues.)
This is why people like Nikki (as much as I hated her) should have stayed. It's also why Jayne should stay and housemates like Richard and Susie should really be the big contenders for eviction.