How to construct 4 external lines Feynman diagram from 3 external lines Feynman diagram?

From Renormalization talk/idea by Sean Carroll, when he talks about effective field theory:

but then I could construct from that the following diagram with four
lines in it

In previous talks he explained a bit about diagrams and told interactions can be represented by many (even infinite) number of diagrams. Additionally he mentions "in" lines can be changed to "out" ones (anti-particle), but for one particular interaction, the number of external lines remains the same. Above he claims to construct a 4 external legs interaction from a 3 one. What does it mean?

ADDED more context from the video:

let’s imagine you only had Phi cubed in your field theory that would lead to a Feynman diagram that is just this little vertex but then I could construct from that the following diagram with four lines in it… so for the effective field theorist you don’t have a choice when you start writing down terms in your Lagrangian you have to include them all as long as they don’t violate some symmetry or something