What does "gone "must" mean?
It was not, of course, a wild elephant, but a tame one which had gone "must." It had been chained up, as tame elephants always are when their attack of "must" is due, but on the previous night it had broken its chain and escaped.

1)What does "gone "must" mean?

2)What does "their attack of "must" mean?

Please..

Question

What does "gone "must" mean?
It was not, of course, a wild elephant, but a tame one which had gone "must." It had been chained up, as tame elephants always are when their attack of "must" is due, but on the previous night it had broken its chain and escaped.

1)What does "gone "must" mean?

2)What does  "their attack of "must" mean?

Please..

Answer

From Wiktionary:

must

A time during which male elephants exhibit increased levels of sexual activity and aggressiveness (also musth)

Answer

Matt below has the right definition of the word "must". I just wanted to add that "to go noun/adjective" is a phrase we can use to mean "to become noun/adjective". For example: "to go rogue" means "to go off on your own and become a villain"; "to go postal" means "to become crazy and do destructive things"; "to go green" means "to become more environmentally conscious". Of course, if the noun is a location-type word, then it is the usual definition: "to go/move to some location or in some direction".