Neville's broken nose

[sylviablundell2001]

No: HPFGUIDX 85780

Neville's broken nose had the effect of making him mis-pronounce his 
words, the spell coming out as "Stubefy!" It was thus ineffective. If 
a wizard had a natural speech defect, a lisp, for example, or an 
inability to pronounce the letter "r", would this also affect his 
ability to cast spells? Would he have to undergo elocution lessons? 
Or could it be put right by a simple spell?
Sylvia (just curious)