At this point, Teixeira is like the old crafty guy who plays pickup basketball with guys half his age, schooling them with every old trick in the book. He doesn't have elite athleticism and the one-punch knockout power is gone, but he's smart and durable.
That was enough against Smith in his last fight. He weathered early storms from his younger opponent before taking over in the latter rounds and overwhelming the 32-year-old.
The same things will be difficult to do against Santos. The Brazilian throws strikes with the intention to end fights and oftentimes does.