From the first episode "T-Rex Returns", a jeep being converted into a makeshift Triceratops in order to help the parks first Triceratops "Theo" let off steam. Also a funny moment.
During "A Mammoth Undertaking", Nigel cornered by an Elasmotherium in front of him and a mammoth behind him. There's a moment of fear as the audience, and he, wonders which will back down first.
Nigel rushing in to rescue the Microraptor he'd just caught from being trampled in "Dino Birds". With little time to react and nowhere to run, he literally uses himself as a shield to protect it.
Bob and Nigel towing the Jeep back from the Carboniferous swamp using a big damn titanosaur in "A Bug House".
The entire escape scene in the last episode "Supercroc". 6-ton T. rex vs. 6-ton Mammoth vs. 6-ton Alligator (all female, for some reason) Tyrannosaurus vs. Mammoth, and the Deinosuchus almost killing Matilda!