Learn Swedish: Uppskattar han tryggheten, knackar han i trä. - If he appreciates the safety, he knocks on wood.

This is a common way to form an 'if' statement in Swedish without actually using the word om (if). By starting the clause with the verb (Uppskattar han... instead of Om han uppskattar...), it automatically acts as a conditional clause. This is sometimes called a V1 conditional because the verb takes the very first position.

Why is the second half of the sentence knackar han instead of han knackar?

This is the classic Swedish V2 (verb-second) rule in action. The entire first 'if' clause (Uppskattar han tryggheten) counts as the first block of information. Because the main clause's verb must come second, knackar immediately follows the comma, pushing the subject (han) right after it.

In English we say 'knock on wood'. Why does the Swedish sentence use i (in) instead of på (on)?

The fixed Swedish idiom is ta i trä or knacka i trä (literally 'knock in wood'). If you were to say knacka på trä, it would sound like you are physically knocking on a wooden surface to see if someone is home, rather than performing the superstitious action for good luck.

How is the word tryggheten formed from its base word?