Just one letter when writing or one phoneme when speaking can make make the difference between a sentence which is easily understandable and one which is likely to cause at least momentary confusion (and possibly serious confusion, terminal ambiguity or a complete breakdown of communication).
Example 1: A few days ago, a Facebook friend of mine commented on a thread on someone else’s Facebook page, about people’s experiences with the ‘deep web‘, in particular the murkier parts of it, and for some reason Facebook thought I’d be interested in this. One commenter mentioned ‘snuff movies’. (If you don’t know, and are of delicate sensibility, don’t ask and don’t search.) Another then referred to ‘sniff movies’. In the context, it was clear that this was a typo (though what might jokingly be called ‘sniff movies’ actually exist).
Example 2: Creating a sentence using the word ‘predator’, a student said ‘My /pu:p/ was eaten by a predator’. I think she meant ‘/pʌp/’.
What I find interesting here is thinking about just why these mistakes happened, and similar mistakes happen. In the first case, ‘i’ is next to ‘u’ on the keyboard, and ‘sniff’ is a more common word than ‘snuff’ (though, surprisingly, only just). On the other hand, that commenter had already seen the word ‘snuff’ at least once and possibly more times immediately prior to typing that. (On the subject of typos, I recently had to type the Korean surname Choi. I automatically typed ‘Choir’, even though the two words are totally unrelated and sound totally different.) In the second case, /ʌ/ does not occur in Korean. Koreans usually replace it with 어 (approximately /ɒ/) rather than the 우 (/u:/) which this student did. We know (and this student certainly did, from having learned and used the word in the course of the chapter) that the important fact about a predator is that it hunts and eats other, usually smaller, animals (compare coprophagy (delicate sensibility warning)).