Smelled - smelt
The past tense of the verb 'to smell' can be written in two ways - smelled and smelt. OED says "In the pa[st]. tense and p[artici]ple. both smelled and smelt are in use, but the latter is now  the more frequent of the two in British English." In terms of clarity, smelled is a preferable form of the past tense than smelt, because the latter is ambiguous.
- 'To smelt' is a verb to do with metal-working. It means "To fuse or melt (ore, etc.) in order to extract the metal; to obtain or produce (metal) by this process." (OED)
One cannot easily imagine a sentence in which it would be easy to confuse the two words, but if it is possible, it will happen sometimes.
- There are also some more or less obscure nouns smelt
- From the seventeenth century until 1813, when the coin ceased to be minted, a smelt was a slang word for a half-guinea (10/6, or ten shillings and six [old] pence).
- A smelt is also a small fish, classically in British English Osmerus eperlanus, but the name is given to many species of small fish of different genera and indeed families.