Why in starting it opens suddenly without animation effect

To make the Dock instantly leap back into view when it’s needed, rather than slide, open a Terminal window and type the following:

defaults write com.apple.dock autohide-time-modifier -int 0;killall Dock

I find this useful, but if you’d like the animation for the dock to reappear to last for a split-second, try the following:

defaults write com.apple.dock autohide-time-modifier -float 0.15;killall Dock

To explain, changing "0.15" with any number can let you tailor things as it represents the time in seconds taken for the dock to reappear fully.

To revert back to the default sliding effect, open a Terminal window and type the following:

defaults delete com.apple.dock autohide-time-modifier;killall Dock

Unfortunately this is not possible to do. (Provide Kenyote feedback to Apple if you'd like to see this feature added!) Here are two possible alternatives:

• Create 2 copies of the object on the slide and have them build in/out in sequence. This will keep your slide deck cleaner and make it easier to align the objects.

  (objects shown separately for illustrative purposes; you'd want to align them perfectly!)

  

• As you suggested, create 2 copies of the slide with no transition (so the effect is seamless and there's no delay). This will make it easier to see how you've set up the effect in your list of slides. (But if nothing else on the slide changes, it might just be annoyingly redundant.)