When you ask a person questions he doesn't understand and he gets nervous, this is an example of a time when you fluster him.
Origin of flusterMiddle English flosteren, probably ; from Scand, as in Icelandic flaustra, to bustle, hurry
tr. & intr.v.flus·tered, flus·ter·ing, flus·ters
Origin of flusterFrom Middle English flostring, agitation, probably of Scandinavian origin; see pleu- in Indo-European roots.
(third-person singular simple present flusters, present participle flustering, simple past and past participle flustered)
From a Scandinavian (North Germanic) language, akin to Icelandic flaustra (“to be flustered”).