Resist the second peep

side  

In this situation, Black' double hanging connection (aka trumpet connection) can be peeped at a and b

both peeps answered  

White peeps at both and and Black answers twice. Black's shape (a B2 Bomber!) looks rather clumsy and his lump of stones can be further attacked, depending on surrounding conditions, at for example a or b. In this abstract case, Black's group remains rather strong, but still one feels White got too much with her two forcing moves and .

second peep resisted  

At closer inspection, only threatens to cut off two stones. resists. White cannot cut, because there is a ladder here.

resistance against resistance  

If White stretches once and then cuts, Black is the one getting all the forcing moves and a nice strong wall, sacrificing two stones.

resistance against resistance (2)  

The more White stretches, the more interesting it becomes for Black to connect, as the marked stones gain importance by cutting an increasing White group.

order of peep  

Usually it is therefore important in which order to peep. The circled stones are a little weaker and less important here than the squared ones, so it makes sense to peep at b first, making it harder for Black to resist the second peep.