Grow Legs
Something that's likely to be stolen.
Keep an eye on your suitcase, it's liable to grow legs.
Don't let it grow legs
Means to not let a situation, feeling or idea get out of control...
X= "I've been having this feeling for my co-worker and I know it's wrong 'cause I'm married"
Y= "Wow man, I think it's serious, don't let it grow legs"
Y= "Wow man, I think it's serious, don't let it grow legs"
Grow a leg
Seeing something that makes you hard. I.E. third leg. The old kick stand. Tripod.
Your mom makes me grow a leg.
grow arms and legs
To become substantially more complicated, especially when this was unforeseen. Colloquial expression, primarily used in (British) English. Origin: by analogy to human biological development in the womb.
The project seemed simple at first, but now it's starting to grow arms and legs.