Over the time Bill had known the Doctor, she had learned that he had three ways of answering a question. He didn't always follow an exact script, sometimes he was less vague or more fantastical, but his answers fell into three broad categories.
"Doctor, why does that weird little dinosaur thing keep drooling when he looks at us?"
"Have you seen the trees over there? They glitter! Let's go to look at them very quickly, shall we?"
And they ran.
"Doctor, what does that button do?"
"Have you met our new friend Babbajuk? He's in charge of these nice men with guns, but I'm sure we can work it out."
The self-destruct button got pressed, but they worked out a compromise and everyone lived.
"Doctor, who are you?"
"Oh, is that the time? We'd better get on, we're going to be late."
"Doctor, we've got a time machine. We're never late to anything. Doctor? Doctor!"
2. Non-sequitur that become relevant hours--or days--later
"What are you thinking about?"
"A magic haddock."
Bill always got the point when he finally revealed it, sometimes a couple of minutes before he explained, but the hours of not knowing what a magic haddock was were always annoying. Sometimes, it made her want to scream, but she'd learned on the first proper trip with him that pushing for an answer before he was ready never worked. He'd just double down on the random words and that was no good for either of them.
At least category twos were relatively rare.
3. Truth, but sometimes disguised
"Doctor, who is Nardole?"
"He came from the belly of a beast and I built him out of scraps and glue."
Bill eyed Nardole as he pottered around with a kettle. It sounded fantastical, but she was sure it was the truth, just not the truth in a language she could understand.
At the top of a tower on a planet with three purple moons, Bill asked, "Doctor, why are you guarding the Vault? Really, this time."
"I made a promise."
Bill wrinkled her nose. "I know that. What happened to make you promise?"
He looked slightly to the left of her head. "Not what. Who. There was a thing that happened and a person was there and I had to make a promise."
Before she could ask again, something tried to kill them, so she didn't get the full explanation until it was almost too late.
"Doctor," Bill asked, when they were wading through tunnels on a world with no sun. "Why did you take all those photos of my mum?"
"Me? Why did I...why would you ever think I'd do that?" He puffed up into a ridiculous display of offended dignity, which was only slightly marred by the slime dripping from his hair. "You always ask questions at terrible times, have you noticed that?"
Bill shrugged. She had slime in her hair, too, and it was sliding down her neck. "I ask questions at good times, too."
"When? Tell me the last time you asked a question at a non-terrible time."
"My mum," Bill said, recognising a potential category one answer in progress. "Why did you take those photos? I know it was you, so don't even. You're in a mirror in the background in one. I didn't know why when I first saw it, but you've got a time machine so I can do the maths."
The Doctor made a face. It was his irritated face, which meant he'd realised she wasn't going to let go of this one. "You're annoying when you get clever."
"You love it when I get clever, otherwise you wouldn't be my tutor."
His irritated face intensified. "I'm started to regret that."
He sighed. "You seemed to need them and I didn't know what to get you for Christmas."
Bill grinned at him through the slime, because sometimes the Doctor could tell awful, horrific truths that made her want to cry or scream or run away (she never ran away), but sometimes he did this.
He told the truth, and it was a good truth, and it made her feel better.