When the eel throws the ice cream cone at Spongebob, and Plankton is inside his mouth, the bit of ice cream initially present around his nose disappears and reappears between differently angled shots until disappearing altogether.
When Plankton appears on the sand talking thru his megaphone, his bulldozer smokestack is puffing out engine exhaust, but when the little boys tells his Mom someone left a toy bulldozer on the sand, there is no longer smoke coming out of the smokestack.
When Spongebob is placing the kites along the lagoon towards the end, the string on the fourth one shortens significantly between frames as the kids run out to grab the kite strings.