"You will see at glance how messy he eats."<br/><br/>I saw the sentence and I think that <b>messy</b> should be <b>messily</b> because the verb <b>eat</b> here is an intransitive, so adverbs should follow it like eat <b>right</b>.<br/><br/>What do you native English speakers think?<br/><br/>Thank you so much as always and have a good day.