If the distance you move the pen is too small, the speed too slow, it can't recognize the gestures well and you can't operate it in the way you thought.

The boiler was heavily scaled.

Eat up all your spinach!

Boeing developed a flying boat for the Maritime Self-Defense Force.

Paul is always groping women.

Paul ran his hand through his hair.

Paul has dry hair.

What's up, kiddo?

I don't want to do anything risky.

Don't just stand there like a lump, start taking notes!