And there the letter lay, face downward on the seat he had just left, bent and a little crinkled in proof that he had been sitting on it for some minutes past.
Now it doesn't make any difference whether a man meant to take off his trousers or not.

In a crisis, if they are unfastened, he will hold them up.

It's like catching a monkey; you put corn into a narrow-necked basket.

The monkey inserts his arm, fills his hand with corn, and tries to pull it out, but can't unless he lets go of the corn, which he won't do.

So you catch him.