Ilza !
'I swan!'', means ''swear.''
From the archives:
The Oxford English Dictionary has "swan" as a verb, labeled U.S. slang, derived probably (it says) from northern England dialectal "Is' wan," literally "I shall warrant" = I'll be bound; later taken as a mincing substitute for "swear." The first use in print recorded in the dictionary is from the year 1823.
Ilza, Are you moonlighting from the Poetry Archives? Does Stephen know?