Hmm:

The Hermans Hermits song "A must to avoid".
On the first line of the song they were thought by some to be singing:

"She's a muscular boy"

Rather than the actual line which is:

"She's a must to avoid".

I recall this being mentioned in a program on the BBC World Service Radio about 6-8 years back about this particular song being used by UK brain researchers who were studying how the brain functions by using songs like this where the lyrics are commonly misheard by a percentage of the population.

The researcher said at the time that it gave them some very useful [read: "cheap to get"] information on how the brain turns sound into "speech" without needing to use [expensive/time consuming] CAT or MR scans.

The researcher did say what the official term for this "mishearing of lyrics" was, but I can't recall what it was now, but yes, some boffins really did and probably still do, study this.