maybe it's the scene in LBT11 when Cera's shouting sends Petrie tumbling backwards after he asks her if she's mad about not getting the first treesweet on account of the tinysauruses eating them all.
Okay, I think this is the picture before Petrie rolled right into Littlefoot's leg after Cera swatted him with her tail upon turning away in disgust at seeing Tria flirting with her dad.