In his mental state of wild panic, essentially consisting of a steady stream of oh god oh god I’m trapped I’m trapped getoutgetoffgetoffgetOFF-, he doesn’t have the cognitive capacity to simply stop and pull off the chain, and continues to dash on blazing adrenaline, not even feeling the pain of over-using his now-injured arm.He does, however, have the capacity to realize that her movements, due to inertia, are bound to mirror and exaggerate his, and takes a violently sharp turn, trying to break the chain around his throat.
Despite pulling herself over to him, it was really only to try and reach “safe” harbor. Tigresa really didn’t want to know what would happen if, god forbid, he was able to shake her off.
Then he made the right turn. She shrieked and tried to deflect herself, however ineffectually, away from a tree now rushing right into her. She did it with her arm.
The good thing was that she was able to prevent herself from crashing directly into the tree and releasing him. Unfortunately, with all of the force that Luffy was putting out, her arm received a big fracture for its troubles. That was not even mentioning the scrapes and cuts that now bled freely from her side.
“AAAAAURGH!!” La Tigresa shrieked in agony. For a second, she really thought her arm was broken!
In the next second, however, she was on top of his back. Now, at least, she could start yanking back on the chain now looped snugly around his neck. Yes, she was going to try and choke him out. Yes, it would help distract her from the pain of her fractured arm, which was so bad she had tears in her eyes.
Now that the chain was tightened even further, instinct tells him to stop, save his breath, even if he had a good seventy to ninety gallons of air in his lungs. Manny’s screech of agony was enough to snap him out of his primal state, as well, his reasoning coming back to him.
Hooking his fingers around the chain on his throat, he pulls, trying to take pressure off his trachea, or even break the chain. Even if he couldn’t feel the pain just yet, though, the damage to his arm was still there, and it didn’t work as well as it should have, the slashes in his muscle reducing its functionality. It didn’t help that that was a key flex muscle for pulling, either.
Had she slashed the top of his arm, he would have been fine, but luck was not on his side today.