For a given container made of an extremely reflective surface, is it possible to shine a beam of light in, and with no 'fiddling' (i.e. closing the hole, tilting the object) to contain the beam for an infinite amount of time (not a very long time, but such that it will never escape). Consider the following



Something like this. Except I feel like the light will escape given enough time. Also, the object has to be finite in size (infinite is cheating). If there's a proof that no such container exists then that's fine too.

Ignore factors such as dissipation by heat, or quantum tunneling, and just assume a perfect environment with perfect materials.


Question: Can monsters make multiple attacks in a single action?
Answer: In the final rules it's pretty clear: a monster can make multiple attacks only if it has the "Multiattack" action, which always specifies which attacks can be made.

In the case of the Owlbear, it has a Beak and a Claws attack (Claws counts as only one attack). It also has a Multiattack action saying "The owlbear makes two attacks: one with its beak and one with its claws."

If a creature has different attacks but doesn't have Multiattack it has to choose which one to use at each turn.