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In the 1987 Teenage Mutant Ninja Turtles cartoon, we are told

It was a powerful mutagen. It caused whoever touched it to take on the form of whatever animal they had most recently been in contact with. The turtles started becoming human as they had most recently been with Yoshi.

This explains why the turtles become half-human, as Splinter picks them up to clean them.

But Splinter continues...

But Yoshi had most recently been with... the rats.

Except, Yoshi just handled the turtles. Why didn't he turn into a half-turtle too?

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You should specify which TMNT cartoon. – Rogue Jedi Feb 18 at 14:56
the video makes it clear it's the original late 80's cartoon but agree for the sake of readers and in case the video ever dies – NKCampbell Feb 18 at 14:57
Are you asking why Yoshi didn't turn into a turtle, or why Splinter didn't turn into a turtle? – Dave Johnson Feb 18 at 15:17
@DaveJohnson being that Splinter is Hamato Yoshi, I see no difference. – phantom42 Feb 18 at 15:25
He may have just "been with" the rats, but he just handled the turtles. – phantom42 Feb 18 at 20:37
up vote 27 down vote accepted

It's a question of timing, but the answer is in the video.

  1. The turtles were with Yoshi. Yoshi leaves.
  2. Yoshi was with rats.
  3. The turtles touched the mutagen.
  4. Yoshi stepped in the mutagen (note the bare feet).
  5. Yoshi picked up the turtles.

He came into contact with the mutagen after the rats but before the turtles.

(For clarity's sake, Splinter is Hamato Yoshi in some continuities, including the late-80s cartoon the question is referring to. In other continuities, he owned the rat that became Splinter.)

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This is a good point, but the turtles mutate before Yoshi does. – phantom42 Feb 18 at 15:27
@Phantom42 It's best not to apply too much science to a cartoon and a comic 'cause it's unlikely they thought too hard about it. If they were being realistic, it could be related to absorption and mass. Relatively speaking, the turtles were exposed to far more mutagen than Yoshi, likely prompting a faster change. – T.J.L. Feb 18 at 15:33
@T.J.L. It's not that I don't agree with you for the most part, but if we all bought fully into the "relax, it's just a show" argument, this whole site would cease to exist overnight. – Doug Warren Feb 18 at 16:59
It's also not part of the question - "Why isn't Splinter a half-turtle?" and "Why did the turtles transform faster than Splinter?" are two different questions. – T.J.L. Feb 18 at 17:18
@phantom42 - Why shouldn't the turtles mutate first? They're exposed to the mutagen first, and for a longer period of time, and in greater quantities relative to their body mass (they're basically covered in mutagen by the time Yoshi finds them). One could also argue metabolic differences between turtles and humans, or that the mutagen acts at different rates on different species, but I don't think that's necessary. It's clear from the video that the turtles are exposed first; it follows that they should mutate first. – aroth Feb 19 at 1:24

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