That was pretty much exactly what Tadashi was expecting to hear. Shiro blowing it off like there was absolutely nothing wrong and trying to deflect by telling him he worried too much. Well that second part was probably at least a little bit true. He did worry about his siblings a heck of a lot and it had, at least in part, lead to some fairly unhealthy courses of action. Like going crazy and shifting into half-cat to tear through the woods, but this wasn't about him. It was about Shiro clearly forgetting things that should have been easy to remember and also being fairly tired and moody.
"Shiro," he meowed as he too flicked his tail back and forth, "I know there's something wrong and to be honest you aren't hiding it very well." He let that sink in as he watched the firefly he was going to bat at slowly float away. It was still very tempting to go after it. To chase it down and.... do something? He kind of lost his planning after the point of catching it. They didn't taste good so there was no reason to eat those bugs. He knew- he had tried a few different colors of the glowing bugs and none were good. "I worry just the right amount," he lied, "and I'll always be concerned about my siblings or friends dealing with problems. Even if they are too scared to tell me about them."
Eventually his attention was drawn back to Shiro as she batted a firefly away into the darkness. Since talking wasn't exactly working super well maybe a little playing around would help Shiro loosen up and want to tell Tadashi at least some of what was going on. He crouched real low, wiggling his behind just a little bit as he prepared for just the right moment and pounced towards Shiro while she was a little distracted by watching the firefly.