<spoiler>

That

sum''ich (sammych, sandwich, son of a wich, I'm refering to the number 7 )

was mighty hungry

to ( so )

i axed (deleted, chopped, hit with axe)

'im ( him , the number 7 )

'fore (before)

'e (he)

ate 9

The joke is spoken with an accent, like an old guy with false teeth, who is swallowing letters left and right (not pronouncing the whole words)

I omitted  ( 7 ) x 4, from the list, obviously, so he would not eat 9

This is an adaptation of an old (math teachers?) joke:

Why is six(6) afraid of seven(7)? Because 7-8-9 (seven ate nine, swallowed him whole, fur and all, and didn't even chew)

</spoiler>