# These men lie in wait for their own blood—they set an ambush for their own lives

"But these men are more foolish than the birds. They kill themselves with their own traps". This finishes the comparison started in Proverbs 1:17. 

# These men lie in wait for their own blood

"It is as if they are looking for an opportunity to kill themselves" or "They themselves will be killed because they try to kill others". To lie in wait is to hide, ready to do something wicked.

# their own blood

"to kill themselves violently"

# they set an ambush for their own lives

"it is as if they are the ones who are waiting to suddenly attack and kill them"