What do you notice with regard to the words marked with an asterisk? Of what does it remind you in connection with the hissing sounds?
Notice that final [ð] is unvoiced or whispered towards the end; compare what has been said about final [v] and final [z].
A fault, common especially in bad southern English, and found almost invariably in baby speech, is the substitution of [v, f] for [ð, θ]. The baby says [fʌm] for [θʌm], the cockney [nafiŋk] for [nʌθiŋ], [fevə] for [feðə]. This fault should on no account be tolerated; the child (we are of course not referring to the baby) can produce the lisping sounds without difficulty. It need only be told to place the tongue between the teeth. When once the difference in the manner of production of [f] and [θ] is known, the child can also hear the difference; all that is now required is perseverance.
In careless speech [h] is sometimes substituted for [θ], thus I think so becomes [ai hiŋk sou]. This also has its parallel in baby speech, e.g. [hugə] for sugar.
32. The liquids.—This designation comprises the r sounds and the l sounds.
The sounds written r are extremely varied, and are likely to give some trouble to the student. He should in the first place ascertain from his friends (we are assuming that these speak standard English) whether they notice anything peculiar about his r. If they do not, it is probable that he uses the untrilled r. (The phonetic sign for this is [ɹ], but it is customary to use [r], unless exceptional accuracy be desired.)
This sound is produced by allowing the breath to pass between the raised point of the tongue and the ridge of the upper gums.[34] When the breath makes the tip of the tongue vibrate, we have the trilled or rolled [r]. Can you roll your r? Does anyone you know habitually do so? Have you noticed whether Frenchmen or Germans ever do it?
Another kind of r is that produced at the back of the mouth, by the help of the uvula (see § 8), and called the throat r or uvular r (phonetic sign: [R]), as distinguished from the tongue or teeth r (lingual or dental r). It is not a normal sound in standard English, but is occasionally found. It used to be frequent in Durham and Northumberland (the "Northumbrian burr"), but is dying out there now.