[shanghairay]

[ QUOTE ]
6) How did Shia decide that shoving the All Spark into Megatron's chest would have the same effect as shoving it into Optimus Prime's chest?

[/ QUOTE ]
he took a risky gamble...

but in the dialogue with prime, prime never says it might kill him, he said it would be a sacrafice of himself, so he could only assume it was 100% (or at least very probable) that it would kill him. i mean he basicly takes everything prime says to him as fact throughout the whiole movie so of course he would trust him on it.