Astrophage not moving?

Hey all,

Watched and loved the movie. Not much of a reader so I haven't read the books. There was one thing that confused me in the movie and if someone could shed some light on it, that'll be amaze amaze amaze.

The movie showed how fast the Astrophage moved from the testing plate to the mock Venus box, and afterwards, Grace mentioned that they were at risk of losing the samples when opening the box.

I've noticed there were a few other times in the movie with Grace had them on the testing plate to examine them, and they didn't even move to any other light source—why is it they aren't escaping now? There was also the scene when he collected the samples in the red line between Aidrian and Talceti sun (excuse the spelling), and had them in a syringe as he placed them on the plates. Why didn't they moved then?

Cheers