I cannot think of why there is a contraption under Himiko's body. Any ideas?
A couple things first:
- Himiko was buried c. 248 CE.
- Gears were invented around 100-150 BC (first documented in 4th century).
That being said, during the time of Himiko's burial, the creation and implementation of such machinery would have been considered cutting edge.
Why was the contraption there? Well..
Himiko installed the machinery to scare off anyone that tried moving her body, since she knew that she was a carrier of the disease and was trying to prevent it from spreading. This is the same reason why so many traps and obstacles were in place (as Lara said, to keep someone in and not necessarily out).
Should someone actually make it through all the traps and to Himiko's body, then the machinery would serve to trick the person into thinking that Himiko was cursed and still alive (just as the legend goes), which would hopefully scare the person away.
Initially, the machinery did have this effect on Lara and the group, however, since the movie is set in the 21st century (and people today are much more accustom to modern technology), Vogel caught on quick and revealed the true nature behind Himiko's abrupt movement.
It's possible that, by having the contraption lunge Himiko forward while the person is trying to pick her body up, she would make physical contact with them, thus causing the person(s) to contract the disease and die on the spot, and not have a chance to take her out of the tomb.
From this perspective, the contraption is the last trap of the tomb.