What made Reed Richards elastic in the 2015 Fantastic Four film?

Question

In the 2015 Fantastic Four film,

five people are transformed by Planet Zero. We see how four of them are transformed. Von Doom observes that green lava is alive, like neural tissue that makes the planet a sort of organism. Then Von Doom touches the green neural lava and blends with the planet to the point where he can control matter with his thoughts. Then the others gain lesser powers as part of the storm that is provoked in the wake of this. Ben has rocks fall onto him, so he becomes rock. Jonny gets torched, so he becomes flames. And Sue gets hit by electromagnetic energy, so she gains the ability to control electromagnetic energy. ... Each of those four get hit by specific aspects of the planet, and they each become manifestations of the aspect that hit them individually.

But I do not recall seeing Reed during the act of his transformation. Instead, we just see Reed afterwards in the form in which we would expect if we saw any of the other movies.

So what caused Reed to become elastic in the 2015 film?

Answer 1

From what I recall, the movie didn't show anything specific happening to Reed to give him the power that he ultimately got. My interpretation is that his change didn't happen until after he was back in our universe:

He was trapped beneath a pile of metal and rubble, but he was desperately trying to reach his friend to see if he was OK. Since he couldn't free his legs, his body responded by stretching out to let him move anyway. Whatever force gave him his power responded to what he was "thinking" at the time.

Also note that Sue didn't get hit by anything from Planet Zero that didn't also hit Reed; she was caught in the backwash of the explosion itself, just like the other three. It's possible that her thoughts at the time (maybe "I shouldn't be here" followed by "I could use a blast shield about now") influenced her power as well.

(Yes, I get it, it's thin; it would have been way better for them to just leave all four powers as being random, but unfortunately they did not.)

Answer 2

When Doom fell in the lava, Reed was trying to reach him out. Perhaps he got that power while trying to catch him, literally stretching his arms.

Answer 3

Sues powers came from the energy of planet zero bonding her with the force field of the teleporter, at least that's how I took it...

Reed I have no idea...

I wish the movie would've made a comment that the energy of the planet made their molecular structures unstable, then when they teleported back without the safety measures in place, their molecular structures would've fused with whatever else was in the pods with them.

Johnny with fire, Ben with rocks, Sue with the force field of the teleporter, and because nothing was with Reed his molecules would've stayed in a state of flux (thus stretchy-ness).