A recent fan theory on Reddit reveals a possible explanation for the differences in the regenerations from the old Doctor Who series and the revival.
In the old series, the regenerations weren't exciting. They just happened. However, in the revival, the regenerations are violent. Orange beams shoot out of the Doctor's body.
This new theory suggests that the Sisterhood of Khan, the ones who revived the eighth Doctor and caused him to regenerate into the War Doctor, put something into the regeneration potion that causes the regeneration process to be much more violent. While most would say that the violent regenerations are just to make the show more exciting, I have to agree with this fan theory.
What do you think? Let us know.
Reddit user: anotherandomer