One of the first things Don salvaged from the train was the x-ray machine. He knew a working x-ray would immensely improve the chances of their survival. He no longer had to guess if there were any broken bones or serious internal damage. He could just fire up the x-ray and give a more accurate diagnosis.
He'd been working the past few days to extricate the x-ray machine from the train into his lab in the lair. Now that he hooked up a suitable power source for the machine, he was ready to test it out. Don carefully and methodically layed out all of the items needed for the experimentation.
"Film, check. Protective cover, check. Rubber gloves, check..." Don said. All of the items were ready except for one very important thing.
"OK, now for the test subject." That was going to be the tricky part. Who will be his first willing subject? Master Splinter? Leo? Raph? Mikey? No, they won't do. OK, maybe Mikey but if something went awry during the test and irreversible damage occurred, he would never hear the end of it. While he was debating what to do, Don suddenly felt something brush by his ankle. Quickly looking down, he saw Klunk playfully swishing his tail against his leg. Ah ha! Test subject found!
Don squatted down to pat Klunk's head. While the unsuspecting Klunk mewed contently, Don quickly scooped up the cat and in one swift motion, strapped him tightly onto the extra bed in his lab. The cat recovered from its sudden surprise and started screeching at the top of its lungs. Don quickly closed the lab door so no one, especially Mikey, could hear the cat's call for rescue.
"Sorry, Klunk. I would never ever do this to you except in dire circumstances, and this is one of those circumstances. You are contributing to the survival of our clan. I hope knowing this will make you proud." told Don the distressed cat who did not look proud nor happy to be of any service.
Don quickly got things ready and pressed the button to activate the x-ray. A brief second of the desired exposure and Don turned off the focused radiation and retrieved the film. Yes! He could see clear traces of bone structure and internal organs of a member of the subspecies Felis Catus on the film. Don would have looked at the film more carefully and started analyzing the result if Klunk wouldn't have begun screeching again.
"Oh, I'm so sorry. I'll let you out in a sec". Don first opened the door of the lab and proceeded to remove the straps off the very upset cat.
Klunk shot out of the lab, not even giving one glance back. Looking at Klunk's hasty retreat, Don called out, "My most heartfelt gratitude to your contribution!"
Don couldn't have asked for a better result. The x-ray turned out beautifully. Don decided that it was ready for the real test. Taking a deep breath, he positioned himself on the bed and activated the machine. Doing the same as he did with Klunk, he deactivated the machine after few seconds of exposure and walked over to retrieve the film.
Perfect! He was again able to see the bones and internal organs clearly on the film. He took the film and laid it on his desk next to a book on the anatomy of a normal Red-eared Slider turtle. He started comparing the film against the diagram on the anatomy book carefully, one bone, one organ at a time.
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Michelangelo couldn't figure out why Klunk was so skittish. All evening, he's been trying to lure the cat out of its hiding spot behind the arcade machine in his room. After a long struggle with Klunk, Mikey decided to leave it be and let Klunk come out his own time. Dejected, Mikey walked out of his room down to the living room area. Leo and Raph were preparing for their evening patrol.
'Hey, Mikey, have you seen Don around?" asked Leo
"Not for a while. Remember? He even skipped dinner so I took some leftovers for him in the lab? I don't think he stepped out of his lab at all since lunch," Mikey replied. Mikey's curiosity switch was turned on. What could be so important that Don would lock himself up in the lab and not even come out for dinner?
Suddenly the lab door burst open and Don strode out. His eyes were bloodshot and he had a bit of a wild look about him. He was muttering too. Don didn't even acknowledge his brothers and briskly walked past them without a word towards sensei's room.
'Whas'up with him?" pouted Mikey, eying Don passing by without sparing them a glance.
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Splinter was seated on his straw mat in meditation when he heard a knock. It was about time for the turtle's evening patrol so he was not surprised.
'Come in'.
To his surprise, it wasn't Leonardo who came to tell him that they are leaving for the patrol. Instead, it was Donatello who looked quite stressed and confused.
'My son, what is the matter? Is something troubling you?" asked Splinter wondering what had happened.
'Sensei, I would like to ask you something.", said Don, fidgeting, kept his eyes averted, looking anywhere but his sensei.
'Of course. What would you like to know?". Splinter gestured to Don to sit down who complied.
"Umm, when you first found us, how did you know we were male turtles?" asked Don still his eyes averted, playing nervously with his hands.
'Well, this conversation is taking an interesting turn,' thought Splinter.
"Well, most turtles sold at pet shops are males, so I assumed that you are males. I don't understand why you would be asking this though."
"Do you remember the x-ray machine found in Bishop's train? An X-ray can see the outlines of internal organs. I fixed it up today and took a x-ray shot of Klunk and myself. Well, the picture suggests.. What the internal organs are... I'm a girl!" exclaimed Don. Splinter was shocked. He easily followed most of the story up to the last statement. He felt a powerful urge to confirm what his ears had told him. 'So, I should call you daughter, not son?"
"Yes" answered Don.
"... And your brothers might actually be your sisters?"
"It is possible" again answered Don.
Splinter felt his eyes roll backwards and things suddenly became very dark. His last thought as his consciousness slipped away was, "My sons are now my daughters!?"
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A/N: I got this idea when I read somewhere on Stealthy board that it's hard to determine the sex of a turtle by just looking at it extenally. I don't think Splinter would be biased by gender but I would faint too if I were in same situation :)