Question: How were animals and scenery able to enter the colosseum?
About the article "Colosseum", section "Arena and hypogeum".

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The arena itself was 83 meters by 48 meters (272 ft by 157 ft / 280 by 163 Roman feet).
It comprised a wooden floor covered by sand (the Latin word for sand is "harena" or "arena"), covering an elaborate underground structure called the "hypogeum" (literally meaning "underground").
Little now remains of the original arena floor, but the "hypogeum" is still clearly visible.
It consisted of a two-level subterranean network of tunnels and cages beneath the arena where gladiators and animals were held before contests began.
Eighty vertical shafts provided instant access to the arena for caged animals and scenery pieces concealed underneath; larger hinged platforms, called "hegmata", provided access for elephants and the like.
It was restructured on numerous occasions; at least twelve different phases of construction can be seen.
The "hypogeum" was connected by underground tunnels to a number of points outside the Colosseum.
Animals and performers were brought through the tunnel from nearby stables, with the gladiators' barracks at the Ludus Magnus to the east also being connected by tunnels.
Separate tunnels were provided for the Emperor and the Vestal Virgins to permit them to enter and exit the Colosseum without needing to pass through the crowds.
Substantial quantities of machinery also existed in the "hypogeum".
Elevators and pulleys raised and lowered scenery and props, as well as lifting caged animals to the surface for release.
There is evidence for the existence of major hydraulic mechanisms and according to ancient accounts, it was possible to flood the arena rapidly, presumably via a connection to a nearby aqueduct.
  Fights against wild animals in the arena of the Roman Colosseum were displayed in "Gladiator (2000)" and other films.  
The Colosseum and its activities supported a substantial industry in the area.
In addition to the amphitheatre itself, many other buildings nearby were linked to the games.
Immediately to the east is the remains of the "Ludus Magnus", a training school for gladiators.
This was connected to the Colosseum by an underground passage, to allow easy access for the gladiators.
The "Ludus Magnus" had its own miniature training arena, which was itself a popular attraction for Roman spectators.
Other training schools were in the same area, including the "Ludus Matutinus" (Morning School), where fighters of animals were trained, plus the Dacian and Gallic Schools.
Also nearby were the "Armamentarium", comprising an armory to store weapons; the "Summum Choragium", where machinery was stored; the "Sanitarium", which had facilities to treat wounded gladiators; and the "Spoliarium", where bodies of dead gladiators were stripped of their armor and disposed of.
Around the perimeter of the Colosseum, at a distance of 18 m (59 ft) from the perimeter, was a series of tall stone posts, with five remaining on the eastern side.
Various explanations have been advanced for their presence; they may have been a religious boundary, or an outer boundary for ticket checks, or an anchor for the "velarium" or awning.
Right next to the Colosseum is also the Arch of Constantine. 
Attraction summary.
Guests queue outside the "Franklin Exploration Center", where it is presumed that they are waiting to board a helicopter which will taken them to "Base Station: Wild Arctic".
The queue outside the attraction includes numerous murals of the Arctic animals and scenery as well as various HD TV monitors that show various clips about the Arctic and its animals running on a loop.
Guests then enter the show building. 
The Colosseum has a wide and well-documented history of flora ever since Domenico Panaroli made the first catalogue of its plants in 1643.
Since then, 684 species have been identified there.
The peak was in 1855 (420 species).
Attempts were made in 1871 to eradicate the vegetation, because of concerns over the damage that was being caused to the masonry, but much of it has returned.
242 species have been counted today and of the species first identified by Panaroli, 200 remain.
The variation of plants can be explained by the change of climate in Rome through the centuries.
Additionally, bird migration, flower blooming, and the growth of Rome that caused the Colosseum to become embedded within the modern city centre rather than on the outskirts of the ancient city, as well as deliberate transport of species, are also contributing causes.
One other romantic reason often given is their seeds being unwittingly transported on the animals brought there from all corners of the empire.