I don't understand this
1.Play is a crucial part of development in most young mamals. Rats produce ultrasonic squeaks to prevent their scuffles turning nasty.

2. People laugh on fairground rides or when tickled to flag a play situation, whether they feel amused or not.

From 1st one, I'm not sure "to prevent their scuffles turning nasty"

From the 2nd sentence, I don't know the meaning "when tickled to flag a play situation"

Can anybody explain it me what that means?

Question

I don't understand this
1.Play is a crucial part of development in most young mamals. Rats produce ultrasonic squeaks to prevent their scuffles turning nasty.

2. People laugh on fairground rides or when tickled to flag a play situation, whether they feel amused or not.

From 1st one, I'm not sure "to prevent their scuffles turning nasty"

From the 2nd sentence, I don't know the meaning "when tickled to flag a play situation"

Can anybody explain it me what that means?

Answer

1.scuffle is a friendly fight and rats do that stuff to stop the fight from getting serious!!!

2. to flag means to show that they are in the mood to play

Answer

1. A scuffle is a non-serious fight.  What they are saying is that the sounds will stop the scuffle if it is turning into a serious fight (biting, etc.) where one or both participants may be injured.
2. People laugh on fairground rides and when they are tickled to indicate (show or flag) a play situation.