Here are the solutions to the riddles when you are ready to view them.

https://www.youtube.com/watch?v=72DCj3BztG4

1) Tomato juice
2) The bike would cross into another dimension
3) It is impossible to go around the entire track at exactly twice the speed as your first attempt without a watch
4) The Pygmy Hippo facing backwards in the toilet

Oooo this is so exciting now lets have a look at Thunders answer's above, bet I'm right ,bet I'm right!!:
Well that wasn't what I was expecting at all.

I couldn't find the Panda :-(

I have trouble finding the answers (and I have not watched the solution video yet). My guesses are:

1.) Disagree with JJ, it's tomato soup, probably Campbell.
2.) Bike would not move.
3.) That one requires a formula....I have to think about that one again.
4.) A passenger walking towards the end of the train, to the dining car, while the train is moving.

#3 The panda is in the bathroom..

#1 You uploaded this video because of....?

#5 Because I love Derek Muller, of course! ......and I also gave a link for the solutions.

1. Difficult: My guess is some goo, or sand. Something with an nonlinear flowing behavior.

2. Ambiguous: depends on the gear ratio. In high gear it goes backwards, but in low gear it might just move forwards. Hard to tell without knowing the numbers and doing the math. These kind of problems often pop up in kinematics.

3. Tricky: To double your average speed, you would have to run twice the distance in the time it took you to run one lap. Unfortunately that time has already passed, so you would have to run the second lap infinitely fast.

4. Easy: The outer rim of the wheel that is below the point of contact with the rail. Or me looking for a toilet.

Those are fun!

I knew kirkelicious would get them!