A mid sized dino goes to get a drink from the river. There's a odd pile of rocks partially submerged near by. They waver oddly if you look close at them but with the running water it doesn't notice. It's head dips down and it begins to drink.
Suddenly a long pink tongue lashes out around the dinos neck. It tries to pull back but is over balanced and falls down the bank into the water. The rocks rear up and shimmer revealing a enormous T Rex like shape with three spiny fins running down its back.
A few days later the pile of rocks reappears in the rivers shallows. Basking in the sun as the water slowly flows around it.
Again, you're latched onto the 'pile of rocks' idea when the active camo means no one is going to be seeing
anything,
not even a 'pile of rocks'.
Try this instead:
A mid sized dino goes to get a drink from the river. It's a peaceful day out, no one is around. The dinosaur dips her head dips down and begins to drink.
Suddenly, a long pink tongue lashes out from the water and wraps around the dinos neck. She tries to pull back but is over balanced and falls down the bank into the water. A shimmering from the water reveals an enormous T-Rex like shape with a large spiny fin on her back.
The dino tries to regain her footing but with the muck and silt is dragged deeper into the river by the tongue.
With a final strong yank the tongue disengages and the dino flops over in the water trying to thrash her way back to shore.
It's too late though. A enormous webbed foot with razor sharp claws smashes into the dinos side, crushing her down beneath the water and into the riverbed.
The T Rex like dino calmly stands in the river, the water splashing and foaming around it. After a few minutes the water stills and she dips her head under the water and pulls up the drowned dino. She drags her prey to the waterfall cave where she's made her home to eat in peace, sheltered from the tropical heat.
The river slowly washes away any trace of the brief conflict, leaving only a slightly disturbed bank as the only evidence.
A few days later, a mid-sized dino goes to drink from the water.
It's a peaceful day out.
No one is around.
The dinosaur dips her head dips down and begins to drink...