Starting suddenly (pôr-se a, desatar a)

Starting Suddenly: Pôr-se a

To express that someone suddenly or deliberately starts doing something, use the reflexive verb pôr-se followed by the preposition a and an infinitive. It often describes immediate reactions.

Because pôr is highly irregular, here is a quick reminder of its present and preterite (past) forms:

PronounPresentPreterite (Past)
euponho-mepus-me
tupões-tepuseste-te
ele / ela / vocêpõe-sepôs-se
nóspomo-nospusemo-nos
eles / elas / vocêspõem-sepuseram-se

Notice how pôr-se a sets the scene for unexpected actions:

If I play a harmless prank, you start crying.
Se eu faço uma brincadeira inofensiva, tu pões-te a chorar.
She made a face and the baby started sobbing.
Ela fez uma careta e o bebé pôs-se a soluçar.
I don't understand what this nonsense is, but they started jumping.
Eu não percebo o que é esta palhaçada, mas eles puseram-se a saltar.

Bursting Into: Desatar a

For an uncontrollable, emotional outburst—such as bursting into tears, erupting in laughter, or breaking into a sudden run—use desatar a followed by an infinitive.

While pôr-se a means "to start," desatar a implies a sudden, intense release of energy or emotion. Desatar is a regular -ar verb.

The joke was hilarious, so they burst out laughing uncontrollably.
A anedota era hilariante, por isso eles desataram a rir descontroladamente.
The clowning terrified the boy and he started sobbing.
A palhaçada apavorou o miúdo e ele desatou a soluçar.
The harmless dog terrifies the neighbor and she starts running uncontrollably.
O cão inofensivo apavora a vizinha e ela desata a correr descontroladamente.