Questions & Answers about Они иногда покашливают и позёвывают от скуки.
How does the по- ... -ива- / -ыва- pattern change the meaning of the verbs here?
This circumfix (prefix + suffix combination) adds two specific nuances: the action happens from time to time (intermittent), and it happens mildly or at a low intensity (attenuative). So rather than having loud coughing fits or huge yawns, the people are just giving little, occasional coughs and yawns.
What base verbs do покашливают and позёвывают come from?
They are built from the imperfective verbs кашлять (to cough) and зевать (to yawn). Notice the spelling and stress shift in the root of зевать: when the по- ... -ыва- structure is added, the е changes to a stressed ё, giving us позёвывать.
Since they have the prefix по-, why are these verbs still imperfective?
Usually, adding a prefix like по- to a verb makes it perfective (like смотреть to посмотреть). However, the suffixes -ива- and -ыва- are strong imperfective markers. When a verb takes both simultaneously to create this specific meaning, the suffix 'wins', keeping the verb imperfective. This fits perfectly here because the sentence describes an ongoing, repeated habit (иногда).
Why use от in "от скуки" instead of из-за?