Optimus remained stationary and stayed very perfectly still. Though no danger was present, he still found himself holding his breath. Why? The human had fallen asleep on him.

One of the children, you, (though you were specifically his charge) wanted to talk to him while he did the mindless parts of his work. He agreed easily, thinking the accompaniment of sound would help with his list of tedious tasks.

He hadn't expected you to fall asleep on him, though he was touched. A small feeling of pride welled up in his spark as you felt safe enough with him to have entered a state of vulnerability. You trusted him to keep you safe.

Miko had informed him though, that to wake a sleeping human in such a position was a very offensive act among humans.

So he remained still. Not wanting to offend you or the rest of the humans with thoughtless gestures without care for human culture. He was a role model after all.