Palm/Passion Sunday Questions

Where did the practice of using palms come from (why were they used when Jesus entered Jersusalem?)
An entry in the on-line Catholic Encyclopedia says that many nations have used palm leaves as "an emblem of joy and victory over enemies". And the Jewish people of the time, well-versed in Hebrew Scripture would have been thinking of Psalm 118 when proclaiming Jesus as the one come to save them from their enemies.
The last few verses of Psalm 118 read: (emphasis added)

This is the day the LORD has made; let us rejoice in it and be glad. LORD, grant salvation! LORD, grant good fortune!
Blessed is he who comes in the name of the LORD. We bless you from the LORD'S house.
The LORD is God and has given us light. Join in procession with leafy branches up to the horns of the altar.
You are my God, I give you thanks; my God, I offer you praise.
Give thanks to the LORD, who is good, whose love endures forever.

The custom of commemorating this day with a procession of palms apparently did not develop until about the 9th century, and in countries where palms are not native, pussy willow, yew, boxwood branches or even flowers are used.

Why are the statues and crucifix covered?

Think of it as a 'fast for the eyes', yet one more way to enter into the solemnity of this Holy Week, and remind ourselves that something extraordinary is going on. Whether it is a way to focus on the sorrowful aspects that lead us to the joy of the resurrection, or a more literal interpretation of Jesus being out of the public eye during his last days leading up to his arrest and crucifixion, it certainly gets your attention, doesn't it?