We learned this song at swimming instruction. It is meant to bring the singers gradually deeper into the water until they are eaten ready for their lesson.
As you sing each verse, you go that far into the water. Thus, the 'boa' progressively encircles you, and you go ever deeper into the pool, until glub you're all the way in.
Chorus
I'm being eaten by a boa constrictor
I'm being eaten by a boa constrictor
I'm being eaten by a boa constrictor
And I don't like it at all!
In between the chorus come the lines as given below, with the optional verses "Oh my, it's up to my thigh" between knee and middle, and "Oh darn, it's up to my arms!" after the middle, but before the neck.
Of course, tucked right in beside this in my memory of swimming lessons is "The wheels on the bus go round and round" which must have some deep trauma associated with it, because I shudder even to think about it tangentally.
The classic verses:
Chorus
Oh no! (Oh no!)
It's up to my toe! (It's up to my toe!)
Chorus
Oh gee! (Oh gee!)
It's up to my knee! (It's up to my knee!)
Chorus
Oh fiddle! (Oh fiddle!)
It's up to my middle! (It's up to my middle!)
Chorus
Oh heck! (Oh heck!)
It's up to my neck! (It's up to my neck!)
Chorus
Oh dread, oh dread!
It's up to my ...
(song ends)
rootbeer277 says: Perhaps mention that this is a Shel Silverstein poem?, which I certainly should have, save that I did not know that.