I've seen what I believe is a german expression/idiom twice, in two slightly different forms:

eine Begrüßung, die es in sich hat

and

die Begrüßung hatte es in sich

but I can't find an explanation online. Am I correct that this is an idiom (commonly used or otherwise)? If so, what is the meaning?

I’ve seen what I believe is a German expression/idiom twice, in two slightly different forms:

eine Begrüßung, die es in sich hat

and

die Begrüßung hatte es in sich

but I can’t find an explanation online. Am I correct that this is an idiom (commonly used or otherwise)? If so, what is the meaning?