A Tree might 'grow in Brooklyn' as the book title goes... but, a 'something unexpected' grows in our classroom sink...

Not sure what this says about:  Cleanliness of our classroom sink?  Or the endurance of plant life?  OR better yet... WHY is something growing in our sink?  WHAT could be growing in our sink? Just your ordinary sink at the back of the elementary classroom.  But, 'what is this?'  What type of Plant life?   Why is it growing in our sink?  Maybe I should ask if any of my students have thrown any 'beans' away recently? I guess if the building starts shaking as I hear a booming voice yelling out... "FEE, FI, FOE, FUM"... That I ought to get concerned.