[JBW1949]

I don’t think he meant “spring” on you like that...I think he meant “surprise” you...

[ASA Vet]

I think a mine that propels a grapnel encased charge up into the air before exploding would certainly be a surprise.

Of course he might have meant a Scottish sword. But those were so large it would be hard to hid one, therefore "springing" a surprise would be a real trick.