The BBC has been showing an Advert with two Kids, a Boy and a Girl singing "Twinkle, Twinkle" to their Mother and Grandmother sitting on a sofa. When it get's to the punchline they sing " you'll get ......... .............. in your eye, but for the love of me I can't figure out what it is they say that shocks the Mother and Grannie.

Can anybody fill in the blanks and put me out of my misery.

bird poo

Thanks, I really must get my ears syringed