Vunipola is wary of the threat Samoa will pose

England number eight Billy Vunipola insists Samoa will "smell blood" when they arrive at Twickenham for Saturday's QBE International.

Successive defeats to New Zealand and South Africa have transformed the showdown against the big-hitting Pacific islanders into a game Stuart Lancaster's men dare not lose.

Vunipola is of Polynesian heritage - his father and uncles played for Tonga - and knows the mindset Samoa will adopt as they seek a first victory over England in seven attempts.

"They are going to smell blood. They'll definitely be licking their lips," the Saracens back row said.

"They'll come here knowing they have a sniff of winning the game, but we can't underestimate them.

"You can't go into an international, no matter who you're facing, believing that you have the right to win. We can't afford to do that.

"You can't look at Samoa thinking 'we can step off the accelerator' because that's when things will go wrong."

England are reeling from a fifth successive defeat after a below-par South Africa left Twickenham 31-28 winners to extend their unbeaten run in the fixture to 12 Tests.

Tears ran down Vunipola's cheek during the national anthem, but what followed was comfortably the worst performance of the 22-year-old's 12-cap career.

Head coach Stuart Lancaster had demanded an improvement from his giant back row and while Vunipola showed plenty of courage he was let down by a succession of handling errors, although he was not alone.

"I made too many mistakes and I apologise for that. A lot of the boys, if there is such a thing, were trying a bit too hard," he said.

"After last weekend everyone wanted to prove a point, not only to themselves but to the people watching. We have to start relaxing more.

"Now we definitely need to win against Samoa and Australia for our peace of mind as a team."