Parece que John tem
transformed one finger into a blade in order to stab Sarah in the shoulder. (We can see the wound on Sarah's shoulder in later scenes.) This is somewhat different from the way the Skynet Terminator transforms John; the Terminator presses its hand into John's face and an orange glow appears around its fingers.
Isso tem o efeito de
immobilising and weakening her, and distracting Reese and Pops. As John explains, he can't kill Sarah, because if he does, Pops will be free to detonate the explosives and destroy them all. But he certainly can hurt her. (This is also a probable homage to a scene at the end of Terminator 2, in which the T-1000 similarly stabs Sarah in the shoulder.)
Em cenas posteriores,
Sarah does not appear any different, so it seems John was unwilling or unable to transform her into a Terminator like himself.