Can you suggest a relevant nasty corner case? Consider an unbounded input string (generally less than 1k, but sometimes more than 100k), a phone display large

Can you suggest a relevant nasty corner case? Consider an unbounded input string (generally less than 1k, but sometimes more than 100k), a phone display large enough to display, say, 80-120 glyphs, and a mechanical abbreviation to a few hundred codepoints soon after input, before all expensive processing. What are the nasty corner cases?